How to read a tolerance spec sheet (without calling us three times)

A tolerance spec sheet looks intimidating the first time you see one, but it's really answering one question: how much can this dimension vary before the part stops working for its intended purpose.

The ± notation next to a dimension (e.g. 25.00mm ±0.05) sets the acceptable range — 24.95mm to 25.05mm in that example. Tighter tolerances cost more to hold consistently, which is why we ask what the part actually needs to do before quoting the tightest possible spec by default.

IT grades (IT7, IT8, IT9, and so on) are a standardized shorthand for tolerance bands defined by ISO. Lower numbers mean tighter tolerance. Most general fabrication work sits comfortably in IT9-IT11; precision-fit components usually need IT7 or tighter.

Surface finish callouts (Ra values, typically in micrometers) describe texture, not dimension — how smooth or rough the surface is. A mating or sliding surface usually needs a lower Ra (smoother); a surface that just needs to look presentable can tolerate a higher one.

If a spec sheet you've received doesn't make sense, send it to us directly — we'll walk through it line by line rather than leaving you to guess.