Knowledge Center
Tolerances & Metrology Reference
Fits and tolerances, surface finish (Ra) grades, and GD&T symbols — how to specify and measure parts so they're made right the first time.
Surface Finish (Ra) Chart
The surface roughness reference: ISO grade numbers N1–N12 with their exact Ra in micrometres and microinches, the machining processes that produce each finish, and where each is used. Convert between Ra µm, Ra µin, and N grade at a glance.
GD&T Symbol Library
The 14 geometric characteristics of GD&T (ASME Y14.5) — form, orientation, location, profile, and runout — with each symbol, what it controls, and whether it needs a datum reference. Plus how to read a feature control frame.
Fits & Tolerances
The common ISO 286 preferred hole-basis fits — from loose running (H11/c11) to force fits (H7/u6) — with the fit type and what each is used for, plus how the hole-basis system and IT grades work.