Nuts: forming
Most nuts up to about M24 are cold forged on 4- to 7-station nut formers. Annealed, coated wire is cut into slugs, and each station shapes the slug a little more: square up the ends, form the hex, chamfer, and finally pierce the hole. The result is an unthreaded nut blank with almost no wasted steel. Larger nuts are hot forged from heated bar, or machined from hexagon bar for small batches and special materials.
Nuts: tapping
The internal thread is cut by a tap. On high-speed tapping machines, blanks feed one after another onto a long bent-shank tap that runs continuously, and finished nuts slide off the curved shank. After tapping, nuts are washed and deburred to remove chips and oil.
Class 10 and 12 nuts, and larger class 8 nuts, are then quenched and tempered. Finally, nuts are coated, sorted and packed.
Galvanised nuts are tapped after coating
Hot-dip galvanising adds zinc to the bolt thread, so galvanised nuts are tapped oversize, after galvanising, to leave room for it. The nut thread is then bare steel, protected by the zinc on the bolt. This is why galvanised bolts and nuts must always be used together as a matched set.
Lock nuts
- Nylon-insert lock nuts (DIN 985 / ISO 10511): a nylon ring is pressed into a recess in the nut and rolled in. The bolt thread cuts into the nylon, which grips and resists loosening.
- All-metal lock nuts: the top of the nut is slightly deformed (pinched from two or three sides) after tapping, so it grips the bolt. These work at temperatures where nylon would fail.
- Flange nuts are formed with an integral washer face, sometimes serrated to bite into the joint.
Washers
- Plain washers are punched from steel strip on power presses: the hole is pierced and the outside blanked in one stroke, then the washers are deburred, and plated if needed.
- Hardened washers for structural bolting are quenched and tempered to a set hardness, so they do not dig in or bed down under high preload.
- Spring washers (split lock washers) are coiled from rectangular-section wire, cut, set to the right twist and hardened.
- Wedge-lock washers such as Nord-Lock come in bonded pairs, with cams on the inside faces and radial teeth outside. They are made from hardened steel and keep a bolt tight by tension rather than friction. See our Nord-Lock range.
Blind rivets and rivet nuts
A blind rivet has two parts. The body is cold headed from aluminium, steel or stainless wire and its centre is extruded or drilled to make the hollow sleeve. The mandrel is headed from steel wire, with a groove that sets the break load. The two are assembled by machine. When you set the rivet, the tool pulls the mandrel head into the body until it expands behind the sheet and the mandrel snaps at the groove.
Rivet nuts are cold formed from steel, stainless or aluminium wire, with the internal thread tapped afterwards, then plated or passivated. Explore our blind rivets and rivet nuts.
Indian standards for nuts and washers
- Hex nuts: IS 1363 (Part 3) for product grade C and IS 1364 (Part 3) for grades A and B. Mechanical properties to IS 1367 (Part 6).
- HSFG nuts and washers: IS 6623 heavy hex nuts and IS 6649 hardened washers, used with IS 3757 bolts.
- Prevailing-torque (lock) nuts: functional properties to IS 1367 (Part 8).
- Plain washers: IS 2016. Spring washers: IS 3063.
Plain washers in India are mostly punched on power presses from CR or HR strip; hardened structural washers must be quenched and tempered to the IS 6649 hardness.
Figures are typical values for guidance. For design, inspection and purchase, always follow the current edition of the standard on your drawing.