Cylindrical pins h8 ISO 2338 automatic machines unhardened turned 16 h8x24

The tolerance grade is indicated by numbers ranging from 1 to 18. As the number increases, the size of the tolerance zone increases. The size of the tolerance depends on the nominal dimension. The tolerance system for internal and external dimensions is standardised in accordance with DIN EN ISO 286. The tolerance zones for external dimensions are indicated by lower-case letters followed by numbers.

Free-cutting steels are described in ISO 683-4. A distinction is made between grades not intended for heat treatment, those intended for case hardening, and free-cutting steels intended for tempering. All steels in accordance with ISO 683-4 are easily machinable (turning, drilling, milling) due to their chip-breaking properties. Tensile strengths range from 310 to 900 MPa, depending on the heat treatment.

The term plain indicates a completely untreated, merely oiled, smooth surface for all DIN and ISO screws such as wood screws, hexagon head screws, threaded rods, nuts and many types of washers.