M10 x 1.25 Self Colour 12.9 High Tensile Fine Pitch Socket Cap Screws (Allen Bolts) DIN 912 / ISO 12474

M10 x 1.25 socket cap screws in 12.9 high tensile steel with a plain black self colour finish, also listed as M10 x 1.25 allen bolts, M10 x 1.25 cap head bolts and M10 fine thread bolts. The thread is 10mm across with a fine pitch of 1.25mm, where a standard M10 has 1.5mm. The cylindrical head is up to 16.27mm in diameter and can be tightened down into a counterbore with an 8mm hex key, or left proud of the work surface.

These are made to DIN 912 / ISO 12474. ISO 4762 is the standard for coarse pitch cap screws and ISO 12474 is the fine pitch one, while DIN 912, the older name, is still what most people search for. The full M10 x 1.25 cap head bolt dimensions are in the table above and in the downloadable PDF spec sheet.

We stock 13 lengths, from 16mm to 75mm, with no minimum order. Buy a handful for a repair or full boxes for production, and the price per screw drops as the quantity rises.

Fine pitch or coarse: which M10 do you need?

Both are 10mm across the thread, which is why they get mixed up. The difference is the pitch, the gap from one thread crest to the next: 1.25mm on this screw and 1.5mm on a standard M10, which is on our M10 12.9 socket cap screws page. M10 also comes in a 1mm fine pitch, so check you are after 1.25 and not 1.

A thread pitch gauge is the quick way to check. Hold the leaf marked 1.25 against the thread and it should sit snug with no gaps. With calipers, measure from one thread crest to the crest 8 gaps along: about 10mm means 1.25 pitch and about 12mm means 1.5.

Don't test a screw in a nut to find out. A coarse nut will not fit a fine pitch screw, and forcing it damages both threads.

Why fine pitch is used

Closer threads leave a slightly thicker core in the screw. M10 x 1.25 has a tensile stress area of 61.2mm², against 58mm² for a standard M10 (ISO 898-1), so it holds a little more at the same strength class. The thread also climbs more gently, which makes it less likely to work loose by itself, and each turn moves the screw less, so it adjusts more finely.

There are trade-offs. The thread is shallower, so it cross threads more easily and takes more turns to run in, and it is no substitute for thread locker where vibration is a real problem. Fine pitch is chosen by whoever designed the part, so match the pitch of the screw you are replacing and don't swap it for coarse.

Choosing the length of an M10 x 1.25 cap screw

Length is measured from under the head to the tip, so an M10 x 1.25 x 30 goes 30mm into the work with the head on top. Our range runs from 16mm to 75mm. Up to 40mm the thread runs the whole way.

From 45mm there is a plain shank under the head and about 32mm of thread at the tip. That 32mm is the standard's reference figure, 2 x the diameter plus 12mm, and it is the same at every partially threaded length.

On a partially threaded screw, measure the part you are clamping first. The plain shank should sit inside it, with the thread starting just below, because the shank cannot screw into the hole. If the shank is too long, the screw bottoms out before the head pulls down.

Get it right and the joint is stronger too, because the shank has no thread cut into it and takes sideways load better than the threaded part.

Black self colour 12.9 steel

The minimum tensile strength of class 12.9 is 1220 N/mm² (ISO 898-1, which covers fine pitch threads as well as coarse), against 700 N/mm² for class 70 stainless. That suits machine tools, jigs and fixtures, dies, motorcycle and automotive work, and anywhere strength matters more than rust resistance.

Black self colour means plain steel, which has little protection against rust. The light film of oil these screws usually arrive with is there to protect them in transit and storage, not once they are fitted. Keep them dry, re-oil them or paint the exposed heads if damp is likely, and save them for indoor and dry jobs, or for jobs where rusting is not an issue.

12.9 is a strong grade, but strength alone does not make a joint safe. For lifting, structural or any other safety-critical work, have the joint designed and checked by a competent engineer before choosing these screws.

Common questions about M10 x 1.25 12.9 socket cap screws

What does M10 x 1.25 mean on a screw?

M10 is the 10mm thread diameter and 1.25 is the pitch, the distance in millimetres from one thread crest to the next. A standard M10 has a 1.5mm pitch, so M10 x 1.25 is the fine pitch version. Both are 10mm across, but they are not interchangeable.

Will an M10 x 1.25 screw fit a standard M10 nut or tapped hole?

No. The width across the thread is the same, but the pitch is different, so the threads will not mesh. You need a nut or tapped hole with the same 1.25 pitch, and forcing the wrong one damages both threads.

How can I tell if my bolt is M10 x 1.25 or a standard M10?

Use a thread pitch gauge and find the leaf that sits in the thread with no gaps. Without one, measure with calipers from one thread crest to the crest 8 gaps along: about 10mm is 1.25 pitch and about 12mm is 1.5. M10 x 1 also exists, so check the gauge reads 1.25 and not 1.

What Allen key size fits an M10 x 1.25 black 12.9 socket cap screw?

Use an 8mm hex key, the same as a standard M10 cap screw. The key size comes from the head, not the pitch, and DIN 912 / ISO 12474 sets it separately for each thread diameter.

Can black self colour 12.9 fine pitch screws be used outdoors?

Yes, but expect them to rust, and quickly in the UK's wet weather, because the oil film they arrive with soon washes off. On some jobs that does not matter. If you want the black finish to keep looking good outdoors, though, paint the exposed heads or choose a rust resistant material instead.