Symbols Used on Our Drawings

These symbols are used on the Mechanical Models engine drawings as well as on many other drawings.

Identifies a surface
Means that the indicated surface should be parallel to surface A within 0.10 mm
Means the bore should be perpendicular to surface A within 0.05 mm
Means that the diameter should be concentric to diameter A within 0.03 mm
Specifies the diameter, in mm
Specifies a thread. M3 means a 3 mm standard thread. 7H means a standard class of fit (that is, make it fit). The pitch for standard metric threads are as follows:
Diameter   Pitch
3 mm   0.5 mm
4 mm   0.7 mm
5 mm   0.8 mm
6 mm   1.0 mm
8 mm   1.25 mm
Indicates a surface finish of 1.6 micrometers, the same as 63 micro inches. That's a good turned surface.
Indicates surface finish of 1.6 micrometers. The circle indicates that you should not remove any material, simply use the size and finish that is provided.