Engineering · GD&T
The 14 geometric controls.
Each control on its own page: the symbol, what the tolerance zone actually looks like, how it's inspected, and what it means for the machinist. Ordered the way ASME Y14.5 groups them.
Form
Controls on a single feature with no datum reference — how straight, flat or round it is on its own.
Straightness
Line elements of a surface or an axis within a tolerance zone.
Read the guide →Flatness
A surface between two parallel planes — mating and sealing faces.
Read the guide →Circularity (Roundness)
Each cross-section between two concentric circles.
Read the guide →Cylindricity
The whole cylindrical surface between two coaxial cylinders.
Read the guide →Profile
The most versatile controls — a uniform boundary around the true profile, with or without datums.
Orientation
A feature's angle relative to a datum — always datum-referenced.
Location
Where a feature is relative to datums or other features.
Position (True Position)
The workhorse of hole patterns — with MMC/LMC bonus tolerance.
Read the guide →Concentricity
Removed from ASME Y14.5-2018 (still seen on legacy drawings) — what to use instead.
Read the guide →Symmetry
Removed from ASME Y14.5-2018 (still seen on legacy drawings) — what to use instead.
Read the guide →Runout
Composite controls for rotating parts, checked with an indicator while turning about a datum axis.
Related
The one-page GD&T symbol chart, the true position calculator, and the tolerance stack-up tool.
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