Nuts

A nut is the female half of a threaded joint. It carries the same thread as the screw and it is what you reach for when the hole cannot be tapped — sheet metal, a through hole in plate, anything you need to take apart from both sides.

Plain or locking

A hex nut to DIN 934 / ISO 4032 holds by friction in the thread and by the clamp load you put into the joint. That is enough for a static assembly. It is not enough under vibration, where the joint loses preload and the nut walks off.

A nylon insert lock nut to DIN 985 carries an unthreaded nylon collar above the thread. The screw cuts its own path through the collar, and the friction of nylon against steel resists back-off independently of clamp load. Two consequences worth knowing: the nut needs several threads protruding to engage the collar at all, and the collar loses grip after repeated reuse — treat them as limited-reuse parts. The nylon also caps the working temperature at roughly 120 °C.

Sizing

Nuts are called out by thread, not by spanner size, but the across-flats dimension is what you actually need at the bench. M3 takes a 5.5 mm spanner, M4 takes 7 mm, M5 takes 8 mm. Every listing gives across flats, across corners and thickness in millimetres and inches.

Material

Stainless steel 304. Stainless against stainless is prone to galling — the threads cold-weld under load and seize. Run the nut down slowly, avoid impact drivers, and use a lubricant on anything above M5.