GD&T Symbol Reference.

Constrains a line element of a feature (axis or surface line) to lie within a specified tolerance zone. The zone is two parallel lines for surface, or a cylinder for axis.

Example: A shaft with ⏤ 0.02 means every cross-section axis lies within a 0.02mm cylinder.

Constrains an entire surface to lie between two parallel planes. Cannot exceed the size tolerance — flatness is always tighter than total size.

Example: A machined block with ⏥ 0.05 means the surface lies entirely within 0.05mm thick sandwich of parallel planes.

Constrains every cross-section of a cylinder, cone, or sphere to lie between two concentric circles. Independent at each cross-section — does not constrain axial alignment.

Example: A bearing journal with ○ 0.008 — each cross-section round within 0.008mm radial band.

Composite of straightness, circularity, and parallelism of cylindrical surface elements. Constrains surface between two concentric cylinders.

Example: A hydraulic cylinder bore with ⌭ 0.015 — entire surface within a 0.015mm thick cylindrical band.

Constrains a surface or axis to be parallel to a datum within a specified tolerance zone. Zone is two parallel planes (surface) or a cylinder (axis).

Example: Top face of a block with ∥ 0.05 to datum A (bottom face) — top surface within 0.05mm parallel sandwich relative to bottom.

Constrains a surface, axis, or median plane to be perpendicular (90°) to a datum. Same zone types as parallelism — perpendicular instead of parallel.

Example: A bored hole axis with ⟂ 0.05 to datum A (the face) — axis perpendicular to face within 0.05mm.

Constrains a surface, axis, or median plane to a specified angle (other than 90°) relative to a datum. The basic angle is shown as a basic dimension.

Example: A 30° bevel surface with ∠ 0.1 to datum A — surface within 0.1mm tolerance zone at 30° angle.

The most common GD&T symbol. Constrains the location of a feature axis or center plane to a tolerance zone (cylinder for holes, two parallel planes for slots) at a basic dimension from datums.

Example: Hole pattern with ⌖ ⌀0.1 Ⓜ A B C — each hole axis within ⌀0.1 cylinder at basic location, with bonus from MMC.

→ Calculate true position from X/Y deviations

Constrains the median points of all opposing elements of a feature to a cylindrical tolerance zone coaxial to the datum axis. Removed in ASME Y14.5-2018 in favor of position or runout.

Example: ◎ ⌀0.05 to datum A — derived median axis within ⌀0.05 zone coaxial to datum A.

Constrains the median plane of a slot or planar feature to be symmetric about the datum plane. Also removed in ASME Y14.5-2018 — use position with center plane instead.

Example: ≡ 0.1 to datum A — median plane of slot within 0.1mm sandwich centered on datum.

Combines circularity and concentricity. Measured by indicator on each cross-section as the part rotates 360° about the datum axis. Captures TIR per cross-section.

Example: ↗ 0.05 to A — indicator placed on rotating surface, must not vary more than 0.05mm at any cross-section.

Combines cylindricity and coaxiality. Indicator traverses the full length of the surface (axially) while part rotates. Captures total form + position deviation.

Example: ⌰ 0.1 to A — indicator moves across full length, total reading variation within 0.1mm anywhere.

Constrains line elements (any cross-section) of a complex curve or surface to lie within a tolerance zone bounded by two curves offset from the basic profile.

Example: Airfoil cross-section with ⌒ 0.1 — each cross-section line within 0.1mm zone around basic shape.

The most powerful GD&T symbol. Constrains a 3D surface to lie within a tolerance zone bounded by two surfaces offset from the basic profile. Can replace size, form, orientation, location all in one.

Example: Casting surface with ⌓ 0.5 A B C — entire surface within 0.5mm thick offset shell relative to datums.