Technically reviewed by Vincent, Founder at HEXVARO
Last reviewed
Quick answer
Quick answer: common wrench sizes
An M8 bolt takes a 13 mm wrench, an M10 takes 17 or 16 mm, and an M16 takes 24 mm. Check which standard your bolts follow, because M10, M12, M14 and M22 differ.
| Size | Wrench, DIN (mm) | Wrench, ISO (mm) | Allen key (mm) | Inquiry |
|---|---|---|---|---|
| M6 | 10 | 10 | 5 | Quote this size |
| M8 | 13 | 13 | 6 | Quote this size |
| M10 | 17 | 16 | 8 | Quote this size |
| M12 | 19 | 18 | 10 | Quote this size |
| M16 | 24 | 24 | 14 | Quote this size |
| M20 | 30 | 30 | 17 | Quote this size |
Metric wrench size chart (mm)
Wrench size is the width across flats. DIN covers DIN 933, DIN 931 and DIN 934. ISO covers ISO 4017, ISO 4014 and ISO 4032. The Allen key column applies to DIN 912 and ISO 4762 socket head cap screws.
| Size | Wrench, DIN (mm) | Wrench, ISO (mm) | Allen key (mm) | Inquiry |
|---|---|---|---|---|
| M3 | 5.5 | 5.5 | 2.5 | Quote this size |
| M4 | 7 | 7 | 3 | Quote this size |
| M5 | 8 | 8 | 4 | Quote this size |
| M6 | 10 | 10 | 5 | Quote this size |
| M8 | 13 | 13 | 6 | Quote this size |
| M10 | 17 | 16 | 8 | Quote this size |
| M12 | 19 | 18 | 10 | Quote this size |
| M14 | 22 | 21 | 12 | Quote this size |
| M16 | 24 | 24 | 14 | Quote this size |
| M18 | 27 | 27 | — | Quote this size |
| M20 | 30 | 30 | 17 | Quote this size |
| M22 | 32 | 34 | — | Quote this size |
| M24 | 36 | 36 | 19 | Quote this size |
| M27 | 41 | 41 | — | Quote this size |
| M30 | 46 | 46 | 22 | Quote this size |
| M36 | 55 | 55 | 27 | Quote this size |
Why DIN and ISO wrench sizes differ
ISO changed the width across flats on a few sizes. Thread size stays the same, so the parts still fit the same nut or tapped hole. The difference matters for tools, automated assembly and tight spaces. State the standard on your order if a specific wrench size matters.
Other head types
- Button and countersunk socket screws often use a different Allen key from cap screws of the same thread.
- Flange bolts can use a smaller wrench size than standard hex bolts.
- Structural bolts use a larger heavy hex head.
What to state in an RFQ
- Standard, size, length and class.
- Width across flats, if your tools or assembly equipment fix it.
- Finish, since thick coatings can affect wrench fit.
- Quantity per size. MOQ is 500 pcs per specification.
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 size wrench fits an M8 bolt?
13 mm for both DIN and ISO hex bolts.
What size wrench fits an M10 bolt?
17 mm under DIN and 16 mm under ISO.
What size wrench fits an M12 bolt?
19 mm under DIN and 18 mm under ISO.
What size wrench fits an M16 bolt?
24 mm for both DIN and ISO hex bolts.
What size Allen key fits an M6 socket screw?
5 mm for a DIN 912 or ISO 4762 cap screw.
What size Allen key fits an M8 socket screw?
6 mm for a DIN 912 or ISO 4762 cap screw.
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