Maximum Material Condition (MMC) Explained

Maximum material condition, written with a circled M, is the size condition where a feature contains the most material. For an external feature such as a shaft, that is its largest permitted size. For an internal feature such as a hole, it is its smallest permitted size.

Why MMC is used

MMC is often used when assembly fit matters. A pin needs room to enter a hole, so the drawing can protect the worst-case functional boundary while allowing additional geometric variation as actual feature size moves away from MMC.

Bonus tolerance in plain English

When MMC modifies a geometric tolerance on a feature of size, the stated tolerance applies at MMC. If the actual hole is larger, or the actual shaft is smaller, the feature gains an equal amount of bonus geometric tolerance. The size limits still apply.

Use it deliberately

MMC is not a shortcut for making a tolerance looser. It is a functional decision that ties size and geometry together. It is especially common with position tolerances on clearance holes, pins, and patterns that must assemble.

Example: a clearance hole

⌖⌀0.20MABC

If a hole has a 10.00–10.20 mm size limit, it has 0.20 mm position tolerance at its 10.00 mm MMC size. At 10.10 mm actual size, it gains 0.10 mm bonus tolerance.

Common mix-up

The circled M after a geometric tolerance and a material-boundary modifier after a datum reference do different jobs. Read the cell and its position carefully.

Keep learning