GD&T Symbol Guide
Maximum Material Condition
Describes the size condition where a feature contains the most material: smallest hole or largest pin.
Definition
Maximum Material Condition is the size of a feature when it contains the maximum amount of material within its size limits.
For an internal feature such as a hole, MMC is the smallest allowed size. For an external feature such as a pin, MMC is the largest allowed size.
Application
Use MMC when assembly clearance matters and a feature can be allowed more geometric error as it moves away from worst-case size.
It is common with position and axis perpendicularity, and may apply to certain orientation or straightness axis controls.
Pin And Hole At Worst-Case Material
MMC supports functional gaging by checking whether the worst-case size and geometry still assemble.
3D Tolerance Zone
MMC changes the effective boundary by combining feature size with geometric tolerance, often creating bonus tolerance.
Inspection Method
Functional gages are common because they represent the virtual condition that the feature must not violate.
Inspection compares actual size, geometric error, and any bonus tolerance gained by departing from MMC.
Worked Check: Clearance Hole Bonus
A hole has MMC size 10.00 mm and position diameter 0.20 at MMC. The actual hole is 10.08 mm and measured position error is 0.25 mm.
Bonus
10.08 - 10.00 = 0.08 mm
A larger hole has more clearance and earns bonus tolerance.
Available
0.20 + 0.08 = 0.28 mm
The geometric tolerance grows with the size departure.
Compare
0.25 <= 0.28
The measured position error is acceptable.
The hole passes because its extra size provides enough bonus tolerance for the location error.
Comparison Table
| Feature | MMC | LMC | Why It Matters |
|---|---|---|---|
| Hole | Smallest size | Largest size | Least clearance |
| Pin | Largest size | Smallest size | Most interference risk |
| Slot/tab | Most material size | Least material size | Functional boundary |
Notes
Bonus tolerance equals the difference between the actual feature size and its MMC size.
MMC is about features of size; it is not used on simple surfaces or profile tolerances.