T-slot nuts DIN 508-10 M5x6

For nuts, only a single digit is used, which indicates the maximum strength class of the bolt with which the nut can be used (a strength class 10 nut can be used with an 8.8 or 10.9 bolt, but not with a 12.9 bolt).

Steel is an iron-carbon alloy with a maximum carbon content of 2% by mass. The steels achieve their intended physical and mechanical properties through various hardening, annealing and tempering processes. It is also possible to harden the edge zone by surface hardening, case hardening or nitriding. Well-known steel grades are structural steels, free-machining steels, case-hardening steels, nitriding steels, tempering steels, tool steels and stainless steels.

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.