Home » A4 Stainless Steel Socket Cap Screws - Cap Head Bolts
A4 Stainless Steel Socket Cap Screws - Cap Head Bolts

A4 Stainless Steel Socket Cap Screws - Cap Head Bolts

A4 stainless steel 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, A4 is the marine grade stainless, broadly the same as 316, which stands up to salt and chemicals far better than standard stainless. We stock them across a range of metric sizes, with no minimum order.

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About A4 Stainless Steel Socket Cap Screws

What they are

A4 socket cap screws have a cylindrical head with a recessed hex socket, driven by an Allen key. A4 is the marine grade of austenitic stainless, broadly the same as 316, and the addition of molybdenum is what gives it much better resistance to salt and chemicals than standard stainless. They are made to DIN 912, the international equivalent of ISO 4762, the same standard used across our socket cap screws range.

Where they're used

The internal drive lets you tighten them in tight spaces, or sink them into a counterbored hole so the head sits flush or below the surface. A4 earns its keep anywhere salt is in play, so boats, docks, coastal buildings, swimming pools and outdoor kit near the sea. It is also the sensible pick around chemicals, and in food and brewing work where washdown is constant.

Choosing a grade

A4 is the best choice when the job is near salt, spray or chemicals. If the work is general indoor or outdoor and nowhere near the coast, A2 stainless does the job for less money. And where raw clamping strength matters more than corrosion resistance, 12.9 high-tensile is the one. Not sure which suits your job? Our grade guide runs through it.

Sizes

We stock A4 socket cap screws across a range of metric diameters, from M1.6 up to M12, in all lengths of each. Shorter lengths are fully threaded and longer ones come partially threaded as standard. There is 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.

A4 Socket Cap Screw FAQs

A4 is the marine grade of stainless steel used for fasteners, broadly equivalent to 316 stainless. It contains molybdenum, which is what lifts its resistance to salt and chemicals well above standard stainless, and it is the grade to choose for coastal and marine work.

For practical purposes yes. A4 is the fastener grade designation and 316 is the material designation, and they describe the same family of molybdenum-bearing austenitic stainless. You will see suppliers use the two terms interchangeably on the same product.

A2 (304 stainless) suits general indoor and outdoor use. A4 (316 stainless) adds molybdenum, which gives it much better resistance to salt and chemicals, so it is the pick for marine and coastal work, or where harsh chemicals are in use. Both share the same DIN 912 spec, just a different grade of stainless and different levels of corrosion resistance.

Yes, that is exactly what A4 is for. It handles salt spray, damp coastal air and chemical exposure far better than standard stainless. No stainless is completely immune in harsh salt water over years, but A4 is the right grade for the job and the one boatbuilders and coastal trades use.

Mostly no. A4 is austenitic stainless, which is largely non-magnetic. The cold working process in forming and threading the screws usually leaves a slight magnetic pull, so a weak reaction to a magnet is normal and does not mean the grade is wrong.

Yes. Our A4 socket cap screws are made to DIN 912, the international equivalent of ISO 4762, the same standard used across the socket cap screws range.