⌖ 0 Zero geometric tolerance at MMC

How to verify

It is verified just like a normal position with Ⓜ, but calculating the virtual condition with the geometric tolerance value at zero: the virtual condition coincides exactly with the feature's MMC size. A functional gauge made to that exact MMC size (with no additional clearance) is the most direct verification method in production; with a CMM, the actual bonus available is calculated as the difference between the measured actual size and MMC, and that bonus must cover all the position deviation found.

Workshop guideline values

General

The value in the frame is always 0; with a typical H9 diameter tolerance, the actual bonus available is around 0.04–0.06 mm.

Accuracy

With an H7 tolerance on the feature, the available bonus is usually 0.01–0.025 mm.

High precision

With precision fits (H6 or tighter), the available bonus can drop below 0.01 mm — almost no real allowance.

Guidance only: the drawing's value always wins.

Common mistakes when interpreting it

• Reading the “0” in the feature control frame as if no geometric tolerance at all were allowed: in fact there is some, but it grows with the actual size of the feature instead of being fixed — the “0” is only the value AT MMC.
• Making the feature aiming at the exact nominal of its size dimension: it pays to deliberately bias it toward the side that generates bonus (hole slightly larger, shaft slightly smaller) within its tolerance, to gain position allowance.