GD&T Study Guide 2026

Multiple datum targets simulate a plane on irregular surfaces (like castings) by defining exact contact points rather than relying on full surface contact.

Surface texture, including roughness, waviness, and lay, plays a critical role in GD&T by influencing how mating parts interact. It affects friction, wear, lubrication, sealing, and electrical contact. Specifying appropriate surface texture ensures proper functional contact, prevents premature failure, and achieves desired performance characteristics.

A datum target symbol is a circle divided by a horizontal line; the lower half contains the datum letter and target number (e.g., A1).

An MMC modifier on the FRTZF allows each feature's tolerance zone to increase (bonus tolerance) as the feature departs from MMC, while still maintaining pattern geometry.

Angularity applied to a surface creates a tolerance zone of two parallel planes oriented at the specified angle relative to the datum.

The surface finish symbol, which often includes a checkmark or triangle (e.g., ⧫ or a similar symbol with a numerical value), is used in GD&T to specify the required surface roughness or texture of a feature. It indicates the acceptable range of microscopic irregularities on the surface, which can impact friction, wear, and aesthetic properties.