GD&T Symbols Chart

What it controls: A feature or pattern must lie within a zone around its theoretically exact location.

Typical use: Bolt-hole placement in an assembly.

Datum order matters. Material modifiers may be permitted only in their applicable contexts.

What it controls: On a legacy ASME drawing, controls derived median points of a cylindrical feature relative to a datum axis.

Typical use: A stepped-shaft or coaxial-bore drawing.

Removed in ASME Y14.5-2018. These examples explain the derived-median-point control on older ASME drawings.

What it controls: Controls a derived median plane relative to a datum plane.

Typical use: A slot centred on a datum plane.

Removed in ASME Y14.5-2018. These examples explain the median-plane control on older ASME drawings.

What it controls: An indicated surface or derived feature must stay parallel to a datum.

Typical use: A sliding face parallel to a mounting base.

The tolerance zone depends on whether the callout applies to a surface or a derived feature.

What it controls: An indicated feature must be oriented at 90° to a datum.

Typical use: A bore axis square to a mounting face.

A diameter symbol indicates a cylindrical tolerance zone for an axis.

What it controls: An indicated feature must be oriented at its theoretically exact angle to a datum.

Typical use: A 30° machined face relative to a base.

Specify the nominal angle with the standard’s exact/basic dimension convention.

What it controls: The permitted departure of a line element from a perfect straight line.

Typical use: A guide rail or the axis of a long pin.

A surface line and a derived axis are different applications; read the feature control frame attachment.

What it controls: The whole indicated surface must lie between two parallel planes.

Typical use: A mounting face that must seat evenly.

A form control; it needs no datum reference.

What it controls: Each circular cross-section must lie between two concentric circles.

Typical use: The roundness of a turned journal.

Evaluated section by section; it does not by itself control the entire cylinder.

What it controls: The entire cylindrical surface must fit between two coaxial cylinders.

Typical use: A bearing seat needing consistent form along its length.

Combines aspects of roundness, straightness and taper without referencing a datum.

What it controls: Each nominated line section must fit within a zone around the true profile.

Typical use: An extruded edge contour checked at selected sections.

With datums, profile can also constrain orientation and location.

What it controls: The full surface must fit within a zone around the true three-dimensional profile.

Typical use: A cast or aerodynamic surface.

The datum references and zone disposition determine what is controlled beyond form.

What it controls: Moves more of the profile tolerance zone to one side of the true profile.

Typical use: A cast surface where extra stock is allowed mainly outward.

ASME uses its unequally disposed profile modifier and convention; the numeric direction must be read from Y14.5.

What it controls: Limits variation at each circular section during rotation about a datum axis.

Typical use: A shaft land rotating in a bearing.

The measurement is section-wise; confirm the datum axis and measurement direction.

What it controls: Limits variation across the full indicated surface during rotation.

Typical use: The entire bearing journal or end face of a rotor.

Controls the surface as a whole, including variation along its length.

What it controls: Identifies the real feature from which a datum is established.

Typical use: A mounting plane labelled datum A.

ASME datum references establish a datum reference frame; order and any boundary modifiers matter.

What it controls: Identifies a specified point, line or area used to establish a datum.

Typical use: Three contact pads on a large casting.

A datum target is a specific contact location or region; its shape and size must be defined.

What it controls: States a theoretically exact nominal size, angle or location.

Typical use: The nominal position of a hole pattern.

ASME uses basic dimensions, commonly boxed, to define exact nominal geometry controlled by a geometric tolerance.

What it controls: Relates a geometric requirement to a feature of size at maximum material.

Typical use: A clearance hole that can gain assembly tolerance as it becomes larger.

MMC after an eligible geometric tolerance provides bonus as size departs from MMC. M after an eligible datum reference instead specifies maximum material boundary.

What it controls: Relates a geometric requirement to a feature of size at least material.

Typical use: Protecting minimum wall thickness near a bore.

LMC after an eligible geometric tolerance provides bonus as size departs from LMC. L after an eligible datum reference instead specifies least material boundary.

What it controls: The stated geometric tolerance does not gain size-dependent bonus tolerance.

Typical use: A hole whose location limit must remain constant across its size range.

ASME RFS is generally the default when no material condition modifier follows the tolerance value.

What it controls: Extends the geometric tolerance zone outside the part over a stated height.

Typical use: A threaded hole locating a long mating bolt.

The value after circled P is the minimum projection height from the indicated surface, not hole depth or bonus tolerance. Datum references and basic dimensions define the zone.

What it controls: Limits of size normally impose a perfect-form boundary at MMC on an individual regular feature of size.

Typical use: A shaft or bore that must assemble against an ideal mating boundary.

ASME Rule #1 is a default size/form requirement, not a separate circled-letter modifier. Its stated exceptions and overrides still apply.