HEX HEAD BOLT/NUT STAINLESS, STEEL M10 X 230MM 692739

The IMPA name gives the size and “stainless” only. It does not give the steel grade or the strength class. State them: for example “M10 × 230, A4-70, with nut”. Under ISO 3506, A2 has the corrosion resistance of 304 and A4, which contains molybdenum, that of 316. Class 70 means 700 N/mm² tensile strength, class 80 means 800 N/mm².^[2]

Check the thread length against the job. The IMPA name gives only the diameter and the overall length, so ask the supplier for the thread length of the bolt offered and make sure the parts being clamped leave enough thread for the nut. If you need thread over the whole length, a fully threaded stud or a cut-to-length studding is the item to ask for, not this set.

If the old bolt came out of a tight space, measure its head across flats and give that size on the requisition, so the replacement takes the same spanner.

Mix-ups: the bolt alone, without nut, is 691789 (PCS); the stainless M10 nut alone is 692826; washers are separate codes (stainless plain 694837, stainless spring-lock 695237). The neighbouring sets 692738 and 692740 are 220 mm and 240 mm.

Stainless bolts and their nuts are covered by separate parts of ISO 3506: part 1 for bolts, screws and studs, part 2 for nuts. The marking reads letter-digit-class, for example A4-80: A for austenitic, a digit from 1 to 5 for corrosion resistance, then the property class. Class 50 is annealed and, with machined threads, more prone to thread galling than classes 70 and 80.^[2]

To avoid bimetallic corrosion, use stainless bolts when the parts joined are stainless; they are also suitable for galvanised steel and aluminium parts.^[2]

Stainless threads are prone to galling, which comes from friction and adhesion between the thread faces while they slide. Lubricating the threads and tightening at lower speed reduce it. Choosing different stainless grades for bolt and nut also helps, but the nut must always be stronger than the bolt.^[3]