Fastener listings are full of numbers like DIN 933 and ISO 7380. They are not marketing. Each one is a dimensional standard that fixes the head size, height, thread and tolerances, which is why a DIN 933 M8 from one supplier fits the same spanner as anyone else's.
Here is what the common ones mean and when to reach for each.
Hex head — DIN 933 and DIN 931
The spanner-driven classic. DIN 933 is fully threaded; DIN 931 is partially threaded with a plain shank under the head.
Use hex head where you need real torque. An external hex gives the best grip of any drive and can be turned with a spanner, socket or adjustable — useful when you are working somewhere awkward. The head is bulky and sits proud, so it is a poor choice where looks matter or clearance is tight.
Full or part thread? Full thread is more versatile and grips through the whole stack. A plain shank is better where the joint sees shear load, or where a component needs to pivot on a smooth section rather than ride on threads.
Socket cap — DIN 912
A cylindrical head with an internal hex (Allen) drive. Compact, and it can be counterbored so the head sits flush or below the surface. Because you drive it with a key rather than a spanner, it works in recesses where nothing else fits.
The trade-off is that the socket is easy to round out if the key is worn or slightly undersized. Use a good key, seat it fully, and keep the socket clean.
Button head — ISO 7380
A low, domed head with an internal hex. The head is wider and shallower than a socket cap, which spreads load on softer materials and gives a neat finished look with no sharp corners.
It cannot take the torque of a socket cap — the shallower socket limits it. Choose button head for appearance, for a joint that gets handled, or where a tall head would snag.
A flange button head adds an integral washer face, spreading load further and removing the need for a separate washer.
Cheese head — DIN 84
Parallel-sided cylindrical head with a straight slot. Period-correct for restoration, instrument work and anywhere a modern cross-drive would look wrong. Slotted drives cam out easily under power, so drive them by hand.
Pan head — DIN 7985
A rounded head with a Pozidriv recess. The general-purpose machine screw. Pozidriv resists cam-out far better than Phillips — use a Pozi bit, not a Phillips one, or you will chew the recess.
Setscrews and grub screws
Confusingly, “setscrew” means two different things. In UK fastener trade it usually means a fully threaded hex bolt. In engineering it can mean a headless grub screw that clamps a component to a shaft. Our listings say which.
Security drives
Pin-TORX (TX with an H suffix, such as TX25H) has a pin in the centre of the recess, so a standard TORX bit will not enter. Anything public-facing — signage, gates, playground equipment, exterior fittings — is a candidate. Remember to buy the driver bits at the same time; they are not in most sets.
Choosing quickly
- Maximum torque, access from the side — hex head, DIN 933
- Tight recess or counterbore — socket cap, DIN 912
- Visible and handled — button head, ISO 7380
- Soft or thin material — flange button head, or add a penny washer
- Restoration and period work — slotted cheese head in brass
- Tamper resistance — pin-TORX security button head
And the grade
Head style is only half the specification. The other half is the material — see our guide to choosing between A2 and A4 stainless before you order anything destined for outdoors.
Where to start
Browse Bolts & Set Screws, Screws, Nuts and Washers. Many bolts are sold as sets with matching nuts and washers, which saves working out what pairs with what.