Tolerance

Related terms

GD&T

GD&T is geometric dimensioning and tolerancing, the symbol system defined in ASME Y14.5 and ISO 1101 for controlling the form, orientation, location, and runout of part features relative to datums. It states functional intent more precisely than plus-minus dimensions and often allows larger tolerances where they do not matter.

ISO 2768

ISO 2768 is an international standard for general tolerances that apply to dimensions without an individual tolerance on the drawing. Part 1 covers linear and angular dimensions in classes f, m, c, and v. ISO 2768-m, the medium class, is the most common title block callout.

Surface roughness (Ra)

Surface roughness (Ra) is the arithmetic average of a surface profile's deviations from its mean line, reported in microinches or micrometers. Typical machined surfaces run 63–125 µin (1.6–3.2 µm) Ra, ground surfaces 16–32 µin (0.4–0.8 µm), and seal surfaces often 16 µin (0.4 µm) or finer.