M5 Self Colour 12.9 High Tensile Socket Cap Screws (Allen Bolts) DIN 912 / ISO 4762
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- Standard DIN 912 / ISO 4762
- Grade 12.9
- Drive Hex socket
How to measure DIN 912 / ISO 4762 socket cap screws
Thread size to diameter
- M1.61.6mm
- M22mm
- M2.52.5mm
- M33mm
- M44mm
- M55mm
- M66mm
- M88mm
- M1010mm
| Dimension | Symbol | Value |
|---|---|---|
| Thread size and pitch | d / P | M5 x 0.8 mm |
| Head diameter (max, knurled) | dk | 8.72 mm |
| Head height (max) | k | 5.00 mm |
| Hex socket size | s | 4 mm |
| Socket depth (min) | t | 2.5 mm |
| Thread length, partially threaded lengths (ref.) | b | 22 mm |
| Length, under the head (head not included) | L | 6 to 180 mm (32 lengths) |
| Property class and tensile strength (min) | Rm | 12.9, 1220 N/mm² |
M5 socket cap screws in 12.9 high tensile steel with a plain black self colour finish, also listed as M5 allen bolts, M5 cap head bolts and M5 socket head screws. The cylindrical head is up to 8.72mm in diameter and can either be tightened down into a counterbore or sit proud on the work surface. M5 cap screws are tightened with a 4mm hex key in the socket on top of the head.
The number in M5 is the metric thread diameter, which has no link to the key size. This screw has a 5mm thread but a 4mm socket, so check the table above, or download the PDF spec sheet, to familiarise yourself with the full M5 cap head bolt dimensions. All of them are to DIN 912 / ISO 4762.
We stock 32 lengths, from 6mm to 180mm, 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.
Where M5 12.9 screws are used
The head stands 5mm proud, the same height as the thread diameter, and 12.9 steel carries more load than stainless of the same size. That suits machine tools, jigs and fixtures, dies, motorcycle and automotive work, and anywhere a high strength fastener is needed.
Choosing the length of an M5 cap screw
Count length from just below the head down to the tip, so an M5 x 20 goes 20mm into the work and the head sits on top. The range runs from 6mm to 180mm. Everything up to 25mm is threaded end to end.
Longer screws, from 30mm, have a smooth shank below the head and a threaded end of about 22mm. That 22mm comes from the standard's reference formula, 2 x the diameter plus 12mm, and it stays the same at every length.
With a partially threaded screw, measure the thickness of the part you are clamping carefully before choosing a length. The plain shank should sit inside that part, with the thread starting just below it, because the shank cannot screw into the tapped hole. If the shank is longer than the part is thick, the screw jams at the end of its thread before the head pulls down tight.
Getting the length right also makes the joint stronger. The plain shank is the full diameter of the screw with no thread cut into it, so it is stronger than the threaded section where the parts meet and carries any sideways load better.
Black self colour 12.9 steel
The minimum tensile strength of class 12.9 is 1220 N/mm² (ISO 898-1), against 700 N/mm² for class 70 stainless. M5 in 12.9 is for jobs where 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 choose stainless for outdoor or wet work, or for jobs that do not need the strength of 12.9.
We also stock the same M5 cap screws in A2 stainless for general outdoor use and in A4 stainless near salt water or chemicals. 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 M5 12.9 socket cap screws
What Allen key size fits an M5 black 12.9 socket cap screw?
Use a 4mm hex key. The M5 figure is the thread diameter, not the key size, and DIN 912 / ISO 4762 sets the key size separately for each thread. For comparison, M4 takes a 3mm key, M6 a 5mm key and M8 a 6mm key.
What does 12.9 mean on a socket cap screw?
It is the property class. The 12 sets the tensile strength, nominally 1200 N/mm² with 1220 as the minimum, and the .9 means the yield point is about 90% of that.
How long is the thread on an M5 black 12.9 socket cap screw?
Everything up to 25mm is threaded end to end. From 30mm the thread at the tip is about 22mm long and the rest is plain shank. The 22mm is a standard reference value (2 x the diameter plus 12mm) that holds for every partially threaded length.
Can black self colour 12.9 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 A2 or A4 stainless instead.