# GD&T Characteristic, Datum and Tolerance Zone Reference > Source: https://netray.co/tools/gdt-characteristic-datum-and-tolerance-zone-reference > Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems. > Section: Free Tools ## Short answer Searchable table of the 14 ASME Y14.5 geometric characteristics and key modifiers, with datum requirement, zone shape and when MMC or LMC is allowed. ## Category engineering-plm ## Audience - Design engineer - Quality engineer - Estimator - CMM programmer ## Tool **Kind:** worksheet **Mode:** reference **Columns:** #### Characteristic or symbol **Key:** item **Type:** text #### Group **Key:** group **Type:** text #### Datum reference **Key:** datum **Type:** text #### Tolerance zone **Key:** zone **Type:** text #### Material condition modifiers **Key:** mods **Type:** text #### Practical note **Key:** note **Type:** text **Rows:** **Item:** Straightness **Group:** Form **Datum:** Never **Zone:** Two parallel lines (surface line elements) or a cylinder (derived median line, diameter symbol) **Mods:** MMC or LMC only when applied to a feature of size axis **Note:** Controls a line element or axis, not the whole surface. Surface straightness is checked per line element. **Item:** Flatness **Group:** Form **Datum:** Never **Zone:** Two parallel planes **Mods:** MMC or LMC only when applied to the derived median plane of a feature of size **Note:** Must be smaller than any size tolerance on the same surface to be meaningful. **Item:** Circularity (roundness) **Group:** Form **Datum:** Never **Zone:** Two concentric circles in each cross-section **Mods:** None **Note:** Evaluated one cross-section at a time, so a tapered part can be perfectly round at each section. **Item:** Cylindricity **Group:** Form **Datum:** Never **Zone:** Two coaxial cylinders **Mods:** None **Note:** Combines circularity, straightness and taper in one control. Costly to inspect, use sparingly. **Item:** Profile of a line **Group:** Profile **Datum:** Optional **Zone:** Uniform boundary around the true profile of a cross-section, equally disposed unless noted **Mods:** None normally **Note:** Used for 2D cross-sections such as airfoil sections, where each section is controlled separately. **Item:** Profile of a surface **Group:** Profile **Datum:** Optional **Zone:** Uniform 3D boundary around the true profile, equally disposed unless noted **Mods:** None normally **Note:** With no datum it controls form only. With datums it controls location, orientation and form together. **Item:** Angularity **Group:** Orientation **Datum:** Always **Zone:** Two parallel planes at the basic angle, or a cylinder for an axis **Mods:** MMC or LMC for a feature of size **Note:** Basic angle must be on the drawing, a plus/minus angle tolerance is a different control. **Item:** Perpendicularity **Group:** Orientation **Datum:** Always **Zone:** Two parallel planes 90 degrees to the datum, or a cylinder for an axis **Mods:** MMC or LMC for a feature of size **Note:** Often the right control for a hole axis to a mounting face. **Item:** Parallelism **Group:** Orientation **Datum:** Always **Zone:** Two parallel planes parallel to the datum, or a cylinder for an axis **Mods:** MMC or LMC for a feature of size **Note:** Surface parallelism also limits flatness of the surface to the same value. **Item:** Position **Group:** Location **Datum:** Normally yes **Zone:** Cylinder (diameter symbol), two parallel planes, or other boundary around the true position **Mods:** MMC, LMC or RFS (RFS is the default) **Note:** Replaces coordinate plus/minus tolerancing for most holes and pins. Bonus tolerance applies under MMC or LMC. **Item:** Concentricity **Group:** Location **Datum:** Always **Zone:** Cylinder around the datum axis for derived median points **Mods:** RFS only **Note:** Removed from ASME Y14.5-2018. Still seen on legacy drawings, use position or runout today. **Item:** Symmetry **Group:** Location **Datum:** Always **Zone:** Two parallel planes about the datum center plane for derived median points **Mods:** RFS only **Note:** Removed from ASME Y14.5-2018. Use position or profile instead. **Item:** Circular runout **Group:** Runout **Datum:** Always (axis) **Zone:** Two concentric circles in each circular element, measured with a full indicator movement **Mods:** RFS only **Note:** Checked per cross-section while rotating the part 360 degrees about the datum axis. **Item:** Total runout **Group:** Runout **Datum:** Always (axis) **Zone:** Two coaxial cylinders for a surface, or two planes for a face, over the whole surface **Mods:** RFS only **Note:** Controls circularity, straightness, taper and wobble together. The indicator travels along the surface. **Item:** Maximum Material Condition (MMC) **Group:** Modifier **Datum:** Not applicable **Zone:** Not applicable **Mods:** Applies to a feature of size and datum features of size **Note:** Smallest hole or largest pin. Gives bonus tolerance as the size departs from MMC. **Item:** Least Material Condition (LMC) **Group:** Modifier **Datum:** Not applicable **Zone:** Not applicable **Mods:** Applies to a feature of size and datum features of size **Note:** Largest hole or smallest pin. Used for minimum wall thickness and edge distance. **Item:** Regardless of Feature Size (RFS) **Group:** Modifier **Datum:** Not applicable **Zone:** Not applicable **Mods:** Default under Y14.5-2018 Rule 2 where no modifier is shown **Note:** The tolerance is fixed. The old circle S symbol was dropped in 2009. **Item:** Projected tolerance zone (P) **Group:** Modifier **Datum:** Not applicable **Zone:** Zone extends above the part surface by the stated height **Mods:** Used with position or orientation of a threaded or press-fit hole **Note:** Controls the fastener location where it mates, not the hole in the part. **Item:** Free state (F) **Group:** Modifier **Datum:** Not applicable **Zone:** Not applicable **Mods:** Nonrigid parts **Note:** Tolerance applies before restraint, used for thin or flexible parts. **Item:** Tangent plane (T) **Group:** Modifier **Datum:** Not applicable **Zone:** Plane contacting the high points of the surface **Mods:** Orientation and flatness controls **Note:** Controls the plane of the surface contacts, ignoring form variation of the surface. **Item:** Statistical tolerance (ST) **Group:** Modifier **Datum:** Not applicable **Zone:** Not applicable **Mods:** Requires statistical process control **Note:** Allows a wider tolerance when process control is demonstrated. Rare outside controlled programs. **Item:** Continuous feature (CF) **Group:** Modifier **Datum:** Not applicable **Zone:** Not applicable **Mods:** Several features treated as one **Note:** Treats multiple surfaces or features as a single feature for the control. **Item:** Independency (I) **Group:** Modifier **Datum:** Not applicable **Zone:** Not applicable **Mods:** Cancels the Rule 1 envelope requirement on a feature of size **Note:** Form is then controlled only by the geometric tolerance, not the size limits. **Item:** Rule 1 (envelope principle) **Group:** Rule **Datum:** Not applicable **Zone:** Perfect-form boundary at MMC **Mods:** Individual features of size **Note:** Where size limits are shown, form cannot violate perfect form at MMC. Reduces the need for separate form callouts. **Item:** Rule 2 (RFS default) **Group:** Rule **Datum:** Not applicable **Zone:** Not applicable **Mods:** All geometric tolerances **Note:** Under Y14.5-2018 RFS applies to the tolerance and datum features unless a modifier states otherwise. **Notes:** Summary of ASME Y14.5 concepts for quick lookup. It is a study aid, not a substitute for the standard, which defines exact requirements and exceptions. Check which edition (2009 or 2018) the drawing cites, since concentricity and symmetry were removed in 2018 and some modifier rules changed. A tolerance zone listed as a cylinder applies when the diameter symbol is in the feature control frame. ## Content **Intro:** This table answers the questions that come up on every drawing review: does this control need a datum, what shape is the zone, and can I use MMC? It covers the 14 characteristics in the ASME Y14.5 family plus the common modifiers and the first two rules. **Sections:** #### How to use the reference **Body:** Search for the characteristic or filter by group. The datum column tells you at a glance whether the control must reference datum features: form controls never do, orientation and runout always do, position almost always does, and profile may or may not. The zone column describes the shape of the tolerance zone the measured feature has to fit inside, which drives the inspection method. The modifier column states whether MMC or LMC can apply, which tells you if bonus tolerance is available and whether a functional gauge is an option. **Bullets:** - Form controls: straightness, flatness, circularity, cylindricity. - Orientation controls: angularity, perpendicularity, parallelism. - Location: position, concentricity, symmetry (the last two removed in 2018). - Runout: circular and total, always RFS, measured from a datum axis. #### Zones drive inspection **Body:** A cylindrical zone from a diameter symbol allows the axis to wander in any radial direction, which suits holes and pins. A pair of parallel planes limits a single direction, which suits slots and flat surfaces. A profile zone is a 3D boundary that can be checked with a CMM scan or a template. Understanding the zone also helps estimators: a total runout or cylindricity callout often means a dedicated setup and a slower inspection cycle than a simple size tolerance, which should show up in the quote. #### Modifiers and bonus tolerance **Body:** MMC and LMC apply only to features of size, such as holes, pins, slots and tabs. Under MMC the tolerance grows as the feature moves away from its maximum material size, so a hole produced near its large limit has more position room, matching how a pin would still fit. LMC works the opposite way and is used to protect minimum wall or edge breakout. RFS leaves the tolerance fixed. Form, runout and surface-based controls generally do not take MMC or LMC, except for axis or median plane controls on a feature of size. #### Edition differences **Body:** ASME Y14.5-2018 removed concentricity and symmetry, replaced them in practice with position, profile or runout, and clarified default RFS handling, so the old circle S symbol is not used. ISO GPS (ISO 1101) has a different set of rules, including a default independence principle rather than the envelope rule, so a drawing prepared to ISO needs different interpretation. When you receive a build-to-print package, confirm the standard and edition in the title block before reviewing callouts. **Cta:** If your shop interprets callouts into inspection plans by hand, Netray can help build a private agent that reads drawing characteristics and drafts the plan and gauge list for your engineers to approve. **Faq:** #### Which GD&T controls do not need a datum? **Answer:** The four form controls, straightness, flatness, circularity and cylindricity, never use datums because they only describe the shape of the feature itself. Profile of a line or surface can be used with or without datums. Orientation, location and runout generally require them. #### Can I use MMC on a flatness callout? **Answer:** Only when flatness is applied to the derived median plane of a feature of size, such as the center plane of a slot. When applied to a surface, flatness takes no material condition modifier, because a surface has no size to depart from. #### What happened to concentricity and symmetry? **Answer:** They were removed from ASME Y14.5 in the 2018 revision because they are difficult to measure and rarely express the real functional requirement. Designers now use position, profile or runout instead. They may still appear on older drawings, so a quoting team needs to recognize them. #### What is the difference between runout and position? **Answer:** Runout is measured by rotating the part about a datum axis with an indicator and controls surface variation relative to that axis, always at RFS. Position controls the location of a feature's axis or center within a zone and can use MMC for bonus tolerance. ## Search terms gd&t characteristics table, gd&t datum required chart, gd&t tolerance zone shapes, gd&t cheat sheet, which gd&t symbols need datums, asme y14.5 2018 characteristics, gd&t mmc lmc rfs rules --- Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json