Nut and washer types compared: hex, lock, flange, castle, coupling, cap and HV nuts, flat, spring and structural washers, with their standards

How hex, thin, nylon-insert and all-metal lock, flange, castle, coupling, cap, wing and HV nuts differ, which nut class goes with which bolt, and when to use DIN 125, DIN 127, DIN 7989 and DIN 6916 washers.

Updated October 18, 2026

A nut is chosen for two things: its property class, which must match the bolt, and its form, which decides how it locks, what it bears on and how it is tightened. A washer spreads the load under the nut or head and protects the surface. This guide compares the nut and washer types we supply and the standards they are made to. For the bolt classes themselves, see the bolt grades guide; for screws, the screw types guide.

Which nut class goes with which bolt

Nut classes under ISO 898-2 are one number: the nut class should be at least the first number of the bolt class, so the bolt breaks before the nut thread strips. The usual pairs are in the table; a higher nut class on a lower bolt is always acceptable.

Nut types at a glance

Lock nuts: nylon insert or all-metal

A nylon-insert lock nut to DIN 985 / ISO 10511 has a polyamide ring that grips the bolt thread and resists turning under vibration. It is the usual choice for machinery, trailers and equipment. The ring limits the service temperature, so for hot service such as exhausts, ovens or parts that go through a paint-curing oven, use an all-metal lock nut to DIN 980 / ISO 7042, which locks by a deformed thread instead. Both are prevailing-torque nuts: they turn stiffly all the way on, not only at the end.

Flange, castle, coupling, cap and wing nuts

• Flange nut (DIN 6923 / ISO 4161): the wide flange acts as a built-in washer, so one part fewer is handled; common on sheet steel, ducting and vehicle assemblies.
• Castle nut (DIN 935 / ISO 7035): slots on top line up with a hole drilled through the bolt, and a split pin to ISO 1234 locks the nut positively. Used on pins, linkages and axles that must not back off.
• Coupling nut (DIN 6334): a long hex nut, three times the thread diameter, that joins two lengths of threaded rod or extends a stud.
• Cap nut (DIN 1587): a closed domed end covers the bolt end, for a clean finish and to keep a sharp thread end away from people and cables.
• Wing nut (DIN 315): tightened and released by hand, for covers, clamps and fixtures that are opened often.

HV nuts for structural steelwork

The HV nut to DIN 6915 / ISO 7414 is part of a preloaded structural bolt set with the DIN 6914 HV bolt and DIN 6916 washers. The bolt, nut and washers are supplied and used as one set, because preload depends on the friction of that combination. In Europe these DIN standards have been replaced by EN 14399, and the HV system lives on in EN 14399-4.

Washer types

Inner and outer diameters, thicknesses and weights of these washers are in the washer size tables.

How to order

Give the standard, the thread size, the class and the finish, for example DIN 985 M12 class 8 zinc plated or DIN 125 M16 flat washer. Washers are ordered by the bolt size they fit, not by their own diameter. Carbon steel nuts and washers are quoted plain or zinc plated; for wet and outdoor service choose A2 or A4 stainless steel. Nuts and washers are sold per piece and can be added to a bolt or threaded rod request.