Low hexagon nuts with chamfer ~0,5d ISO 4035-brass nickel-plated M3

The wrench sizes for hexagon bolts and nuts are specified in ISO 272: 1982-01. The nominal wrench size on the workpiece (e.g. bolt, nut) is the same as that on the tool. However, there is some play between the two to allow the tool to be fitted without difficulty. The relationship between the nominal diameter d of the thread and the wrench size s is standardised in EN ISO 4014 and EN ISO 4017 for hexagon bolts, and in EN ISO 4032 for hexagon nuts (dimensions in mm).

Brass is a copper-zinc alloy containing at least 50 per cent copper by mass and up to 45 per cent zinc. Other metals are added to impart specific properties to wrought and cast alloys. Brass is wear-resistant, corrosion-resistant, easily formed both hot and cold, and can be polished. Wrought alloys are used in deep-drawn parts, screws, springs, tubes and instrument components, whilst cast alloys are used in valve bodies, plain bearings and precision engineering components.

Nickel coatings are produced either by electroplating in accordance with DIN EN ISO 4526 or by chemical processes in accordance with DIN EN ISO 4527. In the case of electroplating, there is a risk of hydrogen embrittlement in fasteners with a hardness exceeding 390 HV. This necessitates specific measures (such as annealing), although these do not provide a 100 per cent guarantee against embrittlement.