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Socket Cap Screws - Cap Head Bolts

Socket Cap Screws - Cap Head Bolts

Socket cap screws, also called cap head bolts or Allen bolts, have a cylindrical head with an internal hex drive that you tighten with an Allen key. Made to the DIN 912 standard, also known as ISO 4762, they suit tight or recessed fittings where a spanner won't reach. We stock them in A2 and A4 stainless and 12.9 high-tensile, across a wide range of metric sizes, with no minimum order.

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About Socket Cap Screws

What they are

Socket cap screws, or cap head bolts have a cylindrical head with a recessed internal hex socket and are driven by an Allen key. They're made to DIN 912, the international equivalent of ISO 4762, and are one of the most widely used machine screws in engineering.

Where they're used

The internal drive means you can tighten them in tight spaces, or sink them into a counterbored hole so the head sits flush or below the surface. That makes them handy where there's no room to swing a spanner and where a tidy finish matters. You'll find them on machinery, motorbikes, kit cars, jigs and all sorts of general assembly work.

Choosing a grade

A2 stainless handles general indoor and outdoor use. A4 stainless stands up to salt and chemicals, so it's the one for marine and coastal work. 12.9 high-tensile is the pick where clamping strength matters most. If you're not sure which suits your job, our grade guide runs through it.

Sizes

We stock them across a wide range of metric diameters, from M1.6 up to M24, in plenty of lengths. Shorter lengths are fully threaded and longer ones come partially threaded as standard. There's no minimum order, so you can buy the exact quantity you need. For the full sizing tables and a downloadable PDF, head to our cap head bolt dimensions guide.

Socket Cap Screw FAQs

Yes. Socket cap screws, cap head bolts, socket head cap screws and Allen bolts all describe the same fastener. The name just varies by region, trade etc.

It depends on the screw diameter. The hex socket gets bigger as the screw gets bigger, and the full list of sizes is in our dimensions guide.
Important to note: The M size of the screw is the thread diameter, not the hex key size. The M size and hex key size are not the same.

A2 (304 stainless) suits general indoor and outdoor use. A4 (316 stainless) resists salt and chemicals for marine work. 12.9 is high-tensile steel for maximum strength.

Yes. DIN 912 and ISO 4762 both cover the hex socket head cap screw, and the two references are used interchangeably.

Shorter lengths are fully threaded. Longer lengths come partially threaded as standard.
Where a size is partially threaded, we state that on the size selector option for clarity.

Each of our socket cap screw pages have all applicable sizes available to view.

You can also find them in our cap head bolt dimensions guide, which has the full sizing tables and a downloadable PDF.