In this approach, you can select the smaller outer cylinder to define the feature. Concentricity is expensive to inspect. I have a supplier that has had an issue with concentricity on what is basically bearing bores on either end of a 300 mm long steel tube. When a part needs to be both round and straight along its axis, such as a sliding shaft, or a dynamic locating pin, cylindricity is usually called out. 4(k) of the 2009 edition, we can assume the hole is coaxial with the spherical surface, hence datum E is going to be centered automatically, so the blue dimension is extra and should be deleted, correct? Perpendicularity is a fairly common symbol that requires the referenced surface or line to be perpendicular or 90° from a datum surface or line. To further understand ASME’s reasoning, we searched the 2018 Y14. This area is a cylinder with 0. Unfortunately, concentricity ignores the size, roundness and cylindricity of the feature. It can be. Many people are confused by concentricity callouts. 001" tolerance zone. Tags: None. From what I understand, concentricity seems to include coaxiality, and it is really difficult to measure. Concentricity, and Symmetry, are RFS. • For workpieces with high concentricity callout • For radial readjustment of workpieces with big changes in weight during machining • To apply additional grip force to the workpiece by the adjustment screws • Readjustment of the centerline of the workpiece in process Technical features • Integrated fi ne adjustment to center the. Concentricity is generally reserved for high-precision parts, and only. It's boundary and tolerances are relative to the physical edge of the circle, not the axis line. I just wanted to see how you might handle this concentricity callout in this cavity: Pic11. The feature must be concentric with the axis within 0. Next, you will plot the points on the outer profile’s controlled surface, which can be determined using the CMM or a coordinate measuring machine. Counterbores. 5M-1994 Page 9 of 102 Symbol for: ASME Y14. A requirement that the centerline or axis of two features are located within a specified tolerance of each other. Perpendicularity The GD & T call out below is for a. The concentricity callout (provided it is an ASME Y14. Transforming CMM Metrology with PC-DMIS Pro, CAD and CAD++ software. V-blocks are not the correct datum simulator. 5-2018 define five main types of controls for various part features. If using either the ISO or older ASME standards with the explicit symmetry control symbol (three parallel lines), the control will appear as shown below in a 2D engineering drawing or 3D CAD model: However, for the 2018 ASME standard, both concentricity and symmetry have been replaced with an extended use of the position. U+23FF. I can't remember what the difference is. Runout is what you measure by rotating a part clamped on one cylindrical surface with a dial indicator on another. Location Tolerances Position: position tolerance is the allowed maximum deviation of position from it true location. The concentricity control specifies that there is a 0. 015 to Datum AAlso, concentricity is a shit callout. John Riggins. The greatest maximum-minimum difference is used as the concentricity. In ASME, you cannot have zone modifiers on a symmetry callout or a concentricity callout. Determine if the free state modifier should be specified. 001" referenced to Datum A. If you see a concentricty call out of diametrical tolerance zone of 0. 3. Y14. We can inspect the circularity of the entire product by selecting multiple cross-sections since runout is a 2D callout and can focus on only one cross-section at a time. Any thoughts on how to get Calypso to measure concentricity per ASME Y14. Chamfers do not have to be a 45 degree angle as shown in the picture above, but this is certainly the most common configuration. I just wanted to see how you might handle this concentricity callout in this cavity: Pic11. Concentricity boundary and tolerances EXCLUDE FORM ERROR. ISO: (I have not much exposure), but concentricity is a special case for position and seems legitimate callout with the axis derived/extracted from the pitch diameter being the one controlled. Concentricity Tolerance Zone. Yet we have 14 different types of tolerances in total, which can be anytime. Cylindricity is a fairly common callout for shafts, pins and any critical cylindrical element. That said, if balance matters that much, you'll likely have it tightly controlled with runout anyway, and then balance it after machining. For the the complete list of the first 256 Windows ALT Codes, visit Windows ALT Codes for Special Characters & Symbols. 1 O O 100+0. Within the GDT panel: Oct 25, 2011. Measure Datum A as cylinder. • For workpieces with high concentricity callout • For radial readjustment of workpieces with big changes in weight during machining • To apply additional grip force to the workpiece by the adjustment screws • Readjustment of the centerline of the workpiece in process Technical features • Integrated fi ne adjustment to center the. Default file types. The geometric dimensioning and tolerancing (GD&T) standards in ASME Y14. This is the area where the center of the measured circle must be, to be in tolerance. When applying concentricity as a bore attribute, consider that it does not control circularity. The following formula is used to calculate the concentricity: C =. Rotate the target and measure the maximum and minimum. Any thoughts on how to get Calypso to measure concentricity per ASME Y14. Would a concentricity of +/-. • For workpieces with high concentricity callout • For radial readjustment of workpieces with big changes in weight during machining • To apply additional grip force to the workpiece by the adjustment screws • Readjustment of the centerline of the workpiece in process Technical features • Integrated fi ne adjustment to center the. 2 Concentricity -Concentricity tolerance drawing call out. 4. On the Annotate tab, click Geometric Tolerance. First, you will have to establish and identify where would the point of the datum plane, surface, or axis lies. Concentricity is a special case of coaxiality where multiple features exist on the same plane. It essentially means the same thing — the total variation from highest to lowest gage point. GD&T Professional Geometric Learning Systems . For drawings, click Datum Feature (Annotation toolbar) or Insert > Annotations > Datum Feature Symbol. I just wanted to see how you might handle this concentricity callout in this cavity: Pic11. This block shows how a GD&T callout applies to a feature. ) has to "wrap" around the entire. 2 Concentricity - GD&T symbols with examples. As I posted today in thread entitled "True position callout" there are at least two additional methods of assigning two or more features coaxial: 1. 5 is clear on this. Straightness, Flatness, Circularity, Cylindricity, Line profile, Surface profile, Perpendicularity, Angularity Parallelism, True position, and Concentricity callouts can be added to various created entities and shown in the report. Turning Point Tutors cc Achieving academic excellence Exam Revision Notes MOW 217 Presenter 1: Benji Gwashavanhu Presenter 2:The thread is 1/2-28 if that matters. I have multiple parts where a cylinder is called out as a datum and another cylinder has either a runout or concentricity callout back to the datum. Concentricity b. Concentricity - Concentricity describes a condition in which two or more features (cylinders, cones, spheres, etc. Geometric Dimensioning and Tolerancing is supported in VXinspect if required. Notice the difference in the picture above. In the case of axis parallelism, the zone’s shape is cylindrical which is represented by a diameter symbol in this block. A true position of . I just wanted to see how you might handle this concentricity callout in this cavity: Pic11. See Figure 26. Aerospace engineer working turbine engines for the past decade and a half. Measure other diameter as cylinder. In GD&T, concentricity is a complex tolerance used to establish a tolerance zone for the median points of a cylindrical or spherical part feature . Parallelism is a specific form of angularity only at 0°/180° instead of a called out angle. The tolerance of the perpendicularity callout. For example. Sometimes bore concentricity matters only near the ends, so save money by reflecting that on the drawing. Question: In the following print Gd & T callout for the smaller hole is for a. In theory one might use concentricity for something like a flywheel that needs good dynamic balance, but so far I haven't run across such a situation. The size and alignment of each disc is taken into account. Depth of. The GD&T is telling you what the datum is. To create a feature control frame: Click on the “Annotation” tab. Concentricity is a advanced 3D GD&T call is ensured such one or more component features live concentric about a datum axis. To optimally control and communicate these variations, engineers and manufacturers use a symbolic language called GD&T, short for Geometric Dimensioning and Tolerancing. We can control and measure the location of different features. By default, the previewed GTOL frame is filled with the data of the last placed GTOL within the current part. On a comparitor. The rectangular box that contains a GD&T callout is known as the "feature control frame. RE: Meaning of T on Concentricity KENAT (Mechanical) 2 Feb 12 13:21. 1528 W. A countersink consists of a conical hole that is coaxial to a cylindrical hole, where the angle of the cone is. The shoulder is the ledge between threads and shaft. 4. png. 01mm concentricity call-out on two ID's. . 3. 2 Concentricity -Concentricity tolerance drawing call out. The centerline of your pattern must lie completely within a . 1528 W. It says that each diameter much be concentric with each other and I was trying to avoid having 4 concentricity callouts for each diameter if at all possible. No axis can be perfectly straight. GD&T Symbol: Relative to Datum: Yes MMC or LMC applicable: No Drawing Callout: Description: Concentricity, sometimes called coaxially, is a tolerance that controls the central axis of the referenced feature, to. Symmetry tolerance offers the deviation from that true central datum plane. For drawings, click Geometric Tolerance (Annotation toolbar) or Insert > Annotations > Geometric Tolerance. The top section is the size and shape of the target area. The main bore is 87 mm ID & the piston bore is 80mm. For equal tolerances, a runout callout is always tighter than a concentricity callout. • For workpieces with high concentricity callout • For radial readjustment of workpieces with big changes in weight during machining • To apply additional grip force to the workpiece by the adjustment screws • Readjustment of the centerline of the workpiece in process Technical features • Integrated fi ne adjustment to center the. Concentricity | GD&T Basics The datum, or master feature would be the shaft. Or, can I just get away with using Calypso as is?Manufactured items differ in size and dimensions from the original CAD model due to variations in the manufacturing processes. What I came up with to try and hit a . Description: Concentricity, sometimes called coaxially, is a tolerance that controls the central axis of the referenced feature, to a datum axis. Concentricity is Not Circularity. For most else, other callouts are a better choice. run out d. it needs to point to an actual feature of size. One round of the micrometer. Highlight the required feature in the Feature panel. 001" but concentricity . Countersink vs counterbore. The engineering drawing will indicate which element is the measured surface and which is the datum surface. , it means that the median point(s) cannot be off centre over 0. Screw threads are Class 4g6g. This passage reads “However, two past practices, use of concentricity and use of symmetry symbols, are no longer supported. Measure around the specified circumference. In GD&T jargon, circular runout is commonly known as runout. Let’s look at what concentricity means in CNC machining as well as how it’s measured in both imperial units (inches) and metric. OD/ID Concentricity Callouts Tubing OD/OD concentricity requirements can be indicated on a drawing in several different ways, including: GD&T concentricity symbol, which is a circle within a circle Eccentricity percentage TIR (Total Indicator Reading) Written statements such as “OD and ID must be concentric within 0. 09-16-2008, 09:28 AM. The concentricity tolerance can be evaluated or measured in four basic steps. It says that each diameter much be concentric with each other and I was trying to avoid having 4 concentricity callouts for each diameter if at all possible. What they are doing in QA is the best they can do. Datum Target. Cylindricity is a fairly common callout for shafts, pins and any critical cylindrical element. Concentricity ALT + 10686. " A geometric tolerance shown in a feature control frame is always total, not plus/minus. Measure Datum B as cylinder. 1. Equal mass or inertial concerns are one of the leading causes for the concentricity callout. The groove can be dimensioned for total runout to datum A. Reply replyDatum A is the inside diameter if you see the extended lines on the left inner top and bottom just a poor drawing . The final two places that concentricity is mentioned in. 1. In this question line video, Brandon reviews the differences between the GD&T callouts for circularity, circular runout, and total runout. It comes in useful if a feature is to be defined on a drawing that needs to be uniformly flat without tightening any other dimensions on the drawing. If the operator on the mill measured 0. Figure 26. OD/ID Concentricity Callouts. Fluent with axial and radial stack ups as well as… In this thread, for example, you want to apply concentricity callout to the hole. Measurement requirements for concentricity involves the complex task of mapping the referenced feature by way of opposed point measurements. (** So maybe . You could check the plate hole first screw it in then check the cylinder. Fillet welds. Step-1: Identify and f ix the part on the datum plane/axis/surface. However, when the part is measured using a similar cross-sectional plane, this is considered a case of coaxiality, as. 2 width. GD&T Flatness is a common symbol that references how flat a surface is regardless of any other datum’s or features. The GD&T is telling you what the datum is. Easy Guide to GD&T – Total Runout [ Symbol, Tolerance, Measurement ] GD&T Total Runout Symbol . A 3D scan of the entire surface, combined with expensive software to calculate every median point of every cross section is the only practical way to. Next, the roller body would be rotated in the same setup and have its runout measured in several locations. png. Maximum Material Condition or for short, MMC, is a feature of size symbol that describes the condition of a feature or part where the maximum amount of material (volume/size) exists within its dimensional tolerance. 003" out of center you must multiply this. I know concentricity is obsolete, but I'm curious how you guys would handle this. If I have a callout on a shaft that is 8. The goal is to ensure it is straight enough for the application. V-blocks are not the correct datum simulator. Please, analyse my method to measure the concentricity too, and tell me your opinion. Question 9 of 92 SELECT THE TWO CORRECT ANSWERS: What specifically is this Concentricity callout controlling? O O O +0. For surface parallelism, the zone is made of two parallel planes. Available for all document types. ⏿. The function of concentricity callout is to ensure that the midpoint of two diametrically opposite points lies within a specified tolerance zone. 033 bore to 16/16. Depending on how it is used, it may be. So ideally, both features should share the same true central datum plane. Symmetry is a three-dimensional tolerance that defines two features on a part that are uniform across a datum plane. The broad-brushed intention of this callout is. 9m Create Account. 00" long concent or true position from one OD to Another . If required select feature material modifier. DATUM -A is the 80mm piston bore. What I'm finding is that making the cylinder the datum I get bad results for the runout or concentricity. View Exam Notes ST01 2019MOW. The GD&T standard of Concentricity is not what you might think. We make 'encoder disks' which are disks that have a pattern on them that typically have to be held with a tight tolerance against the ID as204K subscribers in the Machinists community. Older →. Taking 3 points on a CMM using concentricity will construct the ideal circle and give you a better idea of how they will fit. It should be used. Drawing Callout: Description: Concentricity, (called coaxiality in the ISO Standard), is a tolerance that controls the central derived median points of the referenced feature, to a datum axis . Concentricity is, roughly speaking, what you want if you need a shaft to be balanced, but don't need it to be actually round. The purpose of a concentricity callout is to ensure that the midpoint of two diametrically opposite points falls within a specified tolerance zone. 001 for concentricity and . In a drawing view, on a surface that appears as an edge (including silhouette edges) or on a section view surface to identify datum planes in the part. See full list on fractory. The concentricity value for a cylindrical surface is the smallest diameter cylinder that is coaxial with the datum axis and encompasses all of the median points for the entire surface. It is often used in lieu of concentricity and symmetry which also belong to GD&T location controls group. A small flat on the OD of the cylinder would detract from how smoothly the shaft can roll. It has a . It’s a simple issue of uniformity. 005" with the holes that were cut by laser. Therefore, a diameter symbol is not used to call out the RECTANGULAR tolerance zone of the hole center in. I am measuring a cylinder. If a drilled or reamed hole must run perfectly true to a coaxial counterbore or circular boss, a concentricity callout is the best way to assure this. Short tutorial for defining datum and geometric tolerance in Solidworks drawings. Profile tolerances can be used to control location, but these are covered separately. 5 might give you the envelope principle, but how would a reader interpret a concentricity callout, which has a very different meaning in the two systems? John-Paul Belanger Certified Sr. So if your center is 0. It is common to encounter designs where runout, roundness and concentricity might all apply. png. Then measure the other diameter and note the location of its center. The way to correctly tolerance the hole pattern is pretty straight forward. It’s a simple issue of uniformity. Concentricity is juged via AXIS LINE. It's also not in the newest edition. It is a common symbol that references how flat a surface is regardless of any other datums or features. Concentricity: The rings on a bullseye are concentric, just as the wheels on your car are concentric to the axle. Usually the cylinder is checked from outside diameter to inside. It is often used in lieu of concentricity and symmetry which also belong to GD&T location controls group. Step-4: Determine the central points of the plotted profile at various cross. They also allow up to . Concentricity: The rings on a bullseye are concentric, just as the wheels on your car are concentric to the axle. 0005". Instagram: @straighttothepointengineeringDiscord: GD&T Symbol: Relative to Datum: Yes MMC or LMC applicable: No Drawing Callout: Description: Concentricity, sometimes called coaxially, is a tolerance that controls the central axis of the referenced feature, to a datum axis. It says that each diameter much be concentric with each other and I was trying to avoid having 4 concentricity callouts for each diameter if at all possible. Concentricity Gage being used to inspect a part Angularity Measurement • Simple Angle Callout • Use Bevel Protractor – should be anywhere between 29° and 31° Angularity Measurement • Angularity Callout • Tolerance 0. The most common fact you can find about concentricity is that it is not what most people expe. From what I understand, concentricity seems to include coaxiality, and it is really difficult to measure. Chamfer vs fillet. Concentricity: The rings on a bullseye are concentric, just as the wheels on your car are concentric to the axle. The feature must be concentric with the axis within 0. Download a PDF of this procedure: GDT008: Creating GDT Concentricity Call-out Preparation. concentricity: 1 n the quality of having the same center (as circles inside one another) Antonyms: eccentricity a circularity that has a different center or deviates. (The surfaces may be labeled as a datum for use elsewhere, but not in the profile tolerance. Designers and engineers utilize this international language on their drawings to accurately describe part features on the basis of size, form, orientation and location. This symbol gets used with other symbols as well such as counterbores, countersinks, and true position callouts. 0 at the center. 0025’’ lowerthan the center of DBT Hole SizePerpendicularity, Concentricity, and True position callouts may require additional air nozzles, air circuits and multiple input readouts to prevent “out-of-round” conditions from influencing the gage readings. by JoBLOCK. The intended meaning of the . Hold the target in place and put the dial gauge on the vertex of the circumference for the axis for which tolerance is indicated. "Author can do all concentricity callouts for each cylinder ( which will be time consuming ), but over all they just need to have one common axis. ”. The tolerance of concentricity is 0. True position d. The purpose of a concentricity callout is to ensure that the. In terms of programming (code off the top of my head):We would like to show you a description here but the site won’t allow us. The first three characteristics (deviations) may be toleranced either together (in common) by the profile tolerance of the cone ( t in Fig. Concentricity tolerance is a condition in which the axes of all cross-section elements of a feature’s surface of revolution are common to the axis of a datum feature. Taking 3 points on a CMM using concentricity will construct the ideal circle and give you a better idea of how they will fit. use cylindricity and concentricity items from the dimensions toolbar to report per the drawing. Circular Runout VS. Drilling is done first so that it is supported by guide bushing. In GD&T, concentricity is a complex tolerance used to establish a tolerance zone for the median points of a cylindrical or spherical part feature . HTH (Hope This Helps)Datum Selection. 4. Total runout c. These measurements would then need to be compared to each other. When the dimension gains a highlight, release the drag. The ASME standard finally completely dropped concentricity as a callout altogether because everyone was misusing it so much. imgur. 5? As I understand the standard, it is looking for all of the median points of diametrically-opposed elements of the feature. Simultaneous position callouts or MMB/MMC, etc. 5M. concentricity callout. 5M : 29-6-2008Y14. Perpendicularity is a fairly common symbol that requires the referenced surface or line to be perpendicular or 90° from a datum surface or line. 1 Position - The position tolerance symbol is a circle with a horizontal and vertical line drawn through the circle. --This brings up the point that tolerance of position could apply to the bore and not the countersink. This is reasonable from ISO point of view (because ISO concentricity is just a special case of ISO position), but in ASME world concencentricity is something totally different than position, and in this application it would not be proper choice. Drag the tolerance to the existing dimension. This looks like an ISO print so I'm not sure, but this may also be. I would have recommended calling the profile of the hex concentric to the shaft, however seeing as most others here seem to be settled on "profile of a surface" I'll have to re-evaluate my understanding of the concentricity callout. What drafting standard is. Surface perpendicularity does not directly control the angle between the surfaces. Here is an example of a simple but important change to the Fundamental Rules: ASME Y14. For bearings with Normal tolerances in general industrial applications, seats are typically machined to the following tolerances: Shaft seats to grade IT6 dimensional tolerances and grade IT5 total. Observer eye symbol. 1. It says that each diameter much be concentric with each other and I was trying to avoid having 4 concentricity callouts for each diameter if at all possible. Runout, roundness, and concentricity. 16). Look at the most powerful GDT callouts available: Composite Profile and. Post by Tom Oakes » Thu Sep 06, 2018 8:16 pm. 4. 1 SSG, U. In the drwaing below, A and B are the Datums used to establish the center of the hole using the Position Symbol and the. Concentricity is not what you probably think it controls and you should not ever use it. If I construct an axis line from the cylinder and make that line the datum. The software then highlights the actual face once a label is selected and automatically aligns the datum symbol to the size diameter and tolerance callout. This is useful for understanding the GD&T callout. 3. axis and surface d. when its my screw up I have to own up to it just like anyone else. We would like to show you a description here but the site won’t allow us. X and Y values are the sides of a triangle. com readers get an exclusive discount on training! Get the Best GD&T Training Available. Concentricity is the measure of how true a geometric shape is to its ideal form. There's no reconciling it either drawing. Study with Quizlet and memorize flashcards containing terms like For continuous surfaces with a change in use, you must apply the same GD&T across the whole surface or not at all. 1 in this perpendicularity. Concentricity, is a tolerance that controls the central derived median points of the referenced feature, to a datum axis. Definition: The countersink symbol is used to indicate that a countersink hole feature is required. But if he want's to fully go with drawings, he needs to place all concentricity callouts as drawing says. 4 to 5. From the ribbon select Position. It is generally recommended to. ) in any combination have a common axis. 4 mm. The True Position is the exact coordinate, or location defined by basic dimensions or other means that represents the nominal value. The part kept wanting to flex in the 4 jaw. Concentricity would require side B to be measured in all dimensions several times to obtain a full dimensional scan of the surface of the reference feature. The flatness tolerance references two parallel planes (parallel to the surface. jpg and . How to Use True Position. Step-2: Plot the controlled surface outer profile using CMM or other measurement instruments. The map shown above gives the frequency of use of the term «concentricity» in the different countries. Level and origin to that 3D line. Available for all document types. Concentricity, Bullet Alignment, and Accuracy by Bob Kohl concentricity. 4(k) of the 2009 edition, we can assume the hole is coaxial with the spherical surface, hence datum E is. In the ISO standard, it's more or less a position callout, vs the ASME definition which is that the center of all opposing points is within the tolerance zone which is the part that's difficult to measure. How to Measure Concentricity? Concentricity is considered one of the most difficult GD&T traits to measure, due to the challenges in establishing the theoretical central axis. Symmetry is a three-dimensional tolerance that defines two features on a part that are uniform across a datum plane. Unless of course you want two concentric ovals. Concentricity would require side B to be measured in all dimensions several times to obtain a full dimensional scan of the surface of the reference feature. (Reason: concentricity. I would have recommended calling the profile of the hex concentric to the shaft, however seeing as most others here seem to be settled on "profile of a surface" I'll have to re-evaluate my understanding of the concentricity callout. And MachinistGuides. Symmetry. Symmetry tolerance offers the deviation from that true central datum plane. Drawing Callout: Description: Angularity is the symbol that describes the specific orientation of one feature to another at a referenced angle. Use TIR (total indicates runout, the one with two arrows) instead. . I ask because Y14. In GD&T, Total Runout controls how much a feature or surface can vary with respect to a datum if the part is rotated 360 degrees around the datum axis. It can reference a 2D line referenced to another 2D element, but more commonly it relates the orientation of one surface plane relative to another datum plane in a 3-Dimensional tolerance zone. A recommended datum. Using just this one callout, we can control the following physical characteristics. This symbol specifies the depth of a feature. One round of the micrometer. Even if the thru bore and one end bore are done in the same operation with the same tool there could still be issues with concentricity. ASME: concentricity should be replaced with position. 5 drawing) should not even be there. 10-02-2009, 02:34 PM. 1 Fundamental Rules (a)Inserting Datum Feature Symbols. In other words, the GD&T "Position" Tolerance is how far your feature's location can vary from its "True Position". See screen shot below from the machining program. Concentricity: The rings on a bullseye are concentric, just as the wheels on your car are concentric to the axle. 4 mm. In metrology and the fields that it serves (such as manufacturing, machining, and engineering ), total indicator reading ( TIR ), also known by the newer name full indicator movement ( FIM ), is the difference between the maximum and minimum measurements, that is, readings of an indicator, on the planar, cylindrical, or. surface c. Dont take it personal, we all screw up big at times, My favorite screw up is to be . For example, injection-molded medical equipment uses a drastically different set of controls than a high RPM automotive component. The length of the part make it to where parallel would need to be within . In this case, the concentricity callout would be referenced to the journal measurement slice (red band). This callout sets a standard on how straight a feature must be along its length. In all likelihood what your seniors actually want is true position, not concentricity. Specifically, concentricity should generally not be used except under extraordiary circumstance. In the case of an OD-axis concentric to ID-axis datum, it controls the coaxiality between them. A recommended datum. I’m making these parts that call for rough and finish reamers, but I’m having trouble holding to the concentricity callout of . This is useful for understanding the GD&T callout Concentri. Within the GDT panel: Click on the tolerance value to edit. Luckily, we know someone. Please ref to the attached figure, what is the meaning of T on Concentricity callout? Thanks for your assists SeasonLee . If a drilled or reamed hole must run perfectly true to a coaxial counterbore or circular boss, a concentricity callout is the best way to assure this. 12.