GD&T Practice Exam 2026 – Complete Prep Guide

Profile of a surface establishes a tolerance that controls the allowable variation of the entire contour of a surface. This means the tolerance defines an envelope around the intended surface shape, and the actual surface must lie within that envelope as the part is evaluated, often in relation to datums if specified. It treats the surface as a continuous boundary rather than focusing on individual features or holes, and it is not about constructing a datum reference frame or projecting a depth of tolerance. The other descriptions refer to different GD&T concepts—locating a hole pattern, creating a datum frame, or projecting a tolerance zone—rather than governing the full contour of a surface.