Technically reviewed by Vincent, Founder at HEXVARO
Last reviewed · Tables updated
Quick answer
Quick answer: common DIN 912 / ISO 4762 sizes
Pitch, head diameter dk, head height k and hex key size s for the most quoted sizes, read from the complete table below. Head dimensions are maximum values for plain heads.
| Size | Pitch P (mm) | Head diameter dk (mm) | Head height k (mm) | Hex key s (mm) | Inquiry |
|---|---|---|---|---|---|
| M5 | 0.8 | 8.5 | 5 | 4 | Quote this size |
| M6 | 1.0 | 10 | 6 | 5 | Quote this size |
| M8 | 1.25 | 13 | 8 | 6 | Quote this size |
| M10 | 1.5 | 16 | 10 | 8 | Quote this size |
| M12 | 1.75 | 18 | 12 | 10 | Quote this size |
| M16 | 2.0 | 24 | 16 | 14 | Quote this size |
Sourcing these sizes? DIN 912 socket head cap screws Socket head screw supplier
Socket head cap screw dimensions (mm)
Head diameter dk and head height k are maximum values for plain heads. Socket size s is the nominal hex key size. Socket depth t is the minimum key engagement.
| Size | Pitch P | Head diameter dk | Head height k | Hex key s | Socket depth t min | Inquiry |
|---|---|---|---|---|---|---|
| M3 | 0.5 | 5.5 | 3 | 2.5 | 1.3 | Quote this size |
| M4 | 0.7 | 7 | 4 | 3 | 2 | Quote this size |
| M5 | 0.8 | 8.5 | 5 | 4 | 2.5 | Quote this size |
| M6 | 1.0 | 10 | 6 | 5 | 3 | Quote this size |
| M8 | 1.25 | 13 | 8 | 6 | 4 | Quote this size |
| M10 | 1.5 | 16 | 10 | 8 | 5 | Quote this size |
| M12 | 1.75 | 18 | 12 | 10 | 6 | Quote this size |
| M14 | 2.0 | 21 | 14 | 12 | 7 | Quote this size |
| M16 | 2.0 | 24 | 16 | 14 | 8 | Quote this size |
| M20 | 2.5 | 30 | 20 | 17 | 10 | Quote this size |
| M24 | 3.0 | 36 | 24 | 19 | 12 | Quote this size |
| M30 | 3.5 | 45 | 30 | 22 | 15.5 | Quote this size |
| M36 | 4.0 | 54 | 36 | 27 | 19 | Quote this size |
Thread length b (mm)
Short cap screws are threaded to the head. Longer screws are partly threaded with a reference thread length b of about 2d + 12 mm, so an M8 screw has 28 mm of thread and an M12 screw 36 mm. If your design needs full thread on a long screw, say so in the RFQ; it is a special.
| Size | b (ref.) | Size | b (ref.) | Size | b (ref.) | Inquiry |
|---|---|---|---|---|---|---|
| M3 | 18 | M8 | 28 | M20 | 52 | Quote this size |
| M4 | 20 | M10 | 32 | M24 | 60 | Quote this size |
| M5 | 22 | M12 | 36 | M30 | 72 | Quote this size |
| M6 | 24 | M16 | 44 | M36 | 84 | Quote this size |
Hex key sizes across socket screw types
The same thread size takes different keys on different socket screws. Mixing them on one assembly line is a common source of stripped sockets.
| Size | DIN 912 / ISO 4762 cap | ISO 7380-1 button head | DIN 7991 countersunk | Inquiry |
|---|---|---|---|---|
| M4 | 3 | 2.5 | 2.5 | Quote this size |
| M5 | 4 | 3 | 3 | Quote this size |
| M6 | 5 | 4 | 4 | Quote this size |
| M8 | 6 | 5 | 5 | Quote this size |
| M10 | 8 | 6 | 6 | Quote this size |
| M12 | 10 | 8 | 8 | Quote this size |
| M16 | 14 | 10 | 10 | Quote this size |
DIN 912 vs ISO 4762
DIN 912 was replaced by ISO 4762 for coarse threads and ISO 12474 for fine threads. Unlike hex bolts, the head diameter, head height and key size in this chart are the same in both, so DIN 912 and ISO 4762 screws are normally interchangeable for the sizes shown. The DIN number is still what most buyers write; state the standard on your drawing and whether the alternative is acceptable.
Grades, finishes and hydrogen embrittlement
| Grade | Min. tensile (MPa) | Typical finish | Typical use | Inquiry |
|---|---|---|---|---|
| 8.8 | 800 (≤ M16), 830 (> M16) | Zinc plated, black oxide | General machinery | Quote this size |
| 10.9 | 1,040 | Black oxide, zinc flake | Higher-load machinery joints | Quote this size |
| 12.9 | 1,220 | Black oxide (oiled), zinc flake | Tooling, dies, high-load machine frames — the most common cap screw grade | Quote this size |
| A2-70 / A4-80 | 700 / 800 | Plain stainless | Food, marine, chemical, outdoor | Quote this size |
Need these DIN 912 / ISO 4762 sizes? Request a quote
- Class 12.9 is the standard industrial grade for socket head cap screws; it is usually supplied black oxide and oiled.
- Electroplating 10.9 and 12.9 screws brings a risk of hydrogen embrittlement. Zinc flake coatings avoid the electrolytic process and are the usual corrosion-resistant choice for these grades. If you need electroplating, specify baking after plating.
- Stainless socket screws are softer than 12.9 alloy steel and can gall when tightened into stainless threads; consider a lubricant.
Common mistakes to avoid
- Ordering by length including the head. Cap screw length is measured from under the head to the tip; only countersunk screws are measured overall.
- Specifying 12.9 with bright zinc plating and no baking requirement on a safety-relevant joint.
- Assuming a button head or low head screw can replace a cap screw at the same tightening torque. Low head and button head types have reduced head strength.
- Leaving thread length open on long screws when the joint needs thread in a particular place.
How to specify socket head cap screws in your RFQ
- Standard: DIN 912 or ISO 4762 (ISO 12474 for fine threads), with edition if your drawing names one.
- Size × length, e.g. M8 × 30, and full or partial thread if it matters.
- Property class 8.8, 10.9 or 12.9, or stainless A2-70 / A4-80.
- Finish with a full designation: black oxide, zinc flake (e.g. ISO 10683), or zinc plated with baking.
- Quantity per size, packaging (boxes or bulk) and inspection documents such as an EN 10204 3.1 certificate.
Clearance hole and tightening torque
Socket head cap screws are often class 12.9. Torque values are calculated starting points for dry threads, at 75 % of proof load with K = 0.20. Clearance holes are ISO 273 medium series.
| Size | Medium clearance (mm) | Class 8.8 (Nm) | Class 12.9 (Nm) | Inquiry |
|---|---|---|---|---|
| M6 | 6.6 | 11 | 18 | Quote this size |
| M8 | 9.0 | 25 | 43 | Quote this size |
| M10 | 11.0 | 50 | 84 | Quote this size |
| M12 | 13.5 | 88 | 147 | Quote this size |
| M16 | 17.5 | 218 | 365 | Quote this size |
| M20 | 22.0 | 441 | 712 | Quote this size |
| M24 | 26.0 | 761 | 1,231 | Quote this size |
Order these sizes from HEXVARO
Send your size list with grade, finish and quantity — we reply within 2 working hours with price, lead time and shipping terms.
- Reply: within 2 working hours
- MOQ: 500 pcs per specification
- Lead time: 10–15 days stock items
- Payment: T/T · L/C · PayPal
- Shipping ports: Tianjin · Ningbo · Shanghai · Shenzhen
- Incoterms: EXW · FOB · CFR · CIF · DAP
- Experience: Founder with 10+ years in the fastener industry
Frequently asked questions
What Allen key size fits an M8 socket head cap screw?
A 6 mm hex key fits an M8 DIN 912 / ISO 4762 socket head cap screw. M6 uses 5 mm, M10 uses 8 mm and M12 uses 10 mm.
Is DIN 912 the same as ISO 4762?
For the sizes in this chart the head diameter, head height and key size are the same. ISO 4762 is the current international standard; DIN 912 remains the common trade name.
How long is the thread on a DIN 912 screw?
Short screws are threaded to the head. Longer screws have a reference thread length of about 2d + 12 mm: 28 mm for M8, 32 mm for M10 and 36 mm for M12.
Which grade is most common for socket head cap screws?
Property class 12.9 alloy steel with a black oxide finish is the most common industrial choice; 8.8, 10.9 and stainless A2 / A4 are also widely specified.
Can 12.9 socket screws be zinc plated?
They can, but electroplating high-strength screws carries a risk of hydrogen embrittlement. Specify baking after plating, or choose zinc flake or black oxide instead.
What is the MOQ for socket head cap screws?
Reference MOQ is 500 pcs per specification. Stock sizes typically ship in 10–15 days and made-to-order sizes in 25–30 days, subject to quotation.
What hex key fits an M8 socket head cap screw?
A 6 mm hex key. The M8 DIN 912 / ISO 4762 screw has a 13 mm head diameter and 8 mm head height.
What is the head diameter of an M12 socket head cap screw?
18 mm maximum, with a 12 mm head height and a 10 mm hex key.
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