Metric Bolt Size Chart: Pitch, Spanner, Hex Key, Tap Drill
Metric bolt size chart: thread pitch, spanner size, hex key and tap drill
An M8 bolt has a 1.25 mm coarse thread pitch and takes a 13 mm spanner. An M10 bolt to ISO 4017 takes a 16 mm spanner, an M6 socket cap screw takes a 5 mm hex key, and an M8 thread is tapped with a 6.8 mm drill. The tables below give the same figures for every common metric size from M3 to M36.
Coarse pitch, spanner, hex key and tap drill, M3 to M16
| Size | Coarse pitch (mm) | Fine pitch listed on Simfix products (mm) | Spanner, ISO 4017 / ISO 4014 (mm) | Spanner, older DIN 933 / 934 (mm) | Hex key, socket cap ISO 4762 (mm) | Tap drill (mm) |
|---|---|---|---|---|---|---|
| M3 | 0.5 | none listed | 5.5 | 5.5 | 2.5 | 2.5 |
| M4 | 0.7 | none listed | 7 | 7 | 3 | 3.3 |
| M5 | 0.8 | none listed | 8 | 8 | 4 | 4.2 |
| M6 | 1 | none listed | 10 | 10 | 5 | 5 |
| M8 | 1.25 | 1, 0.75 | 13 | 13 | 6 | 6.8 |
| M10 | 1.5 | 1.25, 1 | 16 | 17 | 8 | 8.5 |
| M12 | 1.75 | 1.5, 1.25, 1 | 18 | 19 | 10 | 10.2 |
| M16 | 2 | 1.5 | 24 | 24 | 14 | 14 |
Coarse pitch, spanner and hex key, M20 to M36
| Size | Coarse pitch (mm) | Fine pitch listed on Simfix products (mm) | Spanner, ISO 4017 / ISO 4014 and DIN (mm) | Hex key, socket cap ISO 4762 (mm) |
|---|---|---|---|---|
| M20 | 2.5 | 2, 1.5 | 30 | 17 |
| M24 | 3 | 2, 1.5 | 36 | 19 |
| M30 | 3.5 | 2, 1.5 | 46 | 22 |
| M36 | 4 | 3 | 55 | Simfix does not stock M36 socket cap screws |
How to read the chart
Spanner size is the width across flats, the distance between two opposite flat sides of a hexagon head or nut. ISO 272 sets one series of across flats widths for hexagon head bolts and nuts. A socket cap screw is turned with a hex key that fits its hexagon socket, and the key size is the width across the flats of that socket.
The coarse pitch is the standard thread pitch for each diameter in ISO 262. A fine pitch has a smaller spacing for the same diameter and is only fitted to some products, so check the product page before you buy a fine thread.
Why M10 and M12 have two spanner sizes
ISO 272 changed the across flats widths for M10, M12, M14 and M22 in 1982. M10 changed from 17 mm to 16 mm and M12 from 19 mm to 18 mm. Some DIN 933 and DIN 934 parts still use the older 17 mm and 19 mm sizes. M14 and M22 changed at the same time, so they are not in this chart.
For DIN 933 M10 and M12 set screws, check the product page or email contact@simfix.com for the head size (16 or 18 mm against 17 or 19 mm) before you buy a spanner.
Sizes Simfix stocks
Simfix stocks a fully threaded hexagon head set screw to ISO 4017 in every size in both tables, in both A2 (304) and A4 (316). It stocks ISO 4762 socket cap screws in every size in the tables from M3 to M30, in both grades. It also stocks DIN 933 hexagon head set screws in M10 and M12 in both grades. Sizes were checked against live product data on 20 October 2026.
- Hexagon set screws (ISO 4017 and DIN 933, fully threaded)
- Bolts (ISO 4014 and DIN 931, part threaded)
- Socket screws (ISO 4762 socket cap screws)
- A2 (304) stainless steel fasteners and A4 (316) stainless steel fasteners
Frequently asked questions about bolt sizes
What is the thread pitch and spanner size of an M8 bolt?
An M8 bolt has a standard (coarse) thread pitch of 1.25 mm and takes a 13 mm spanner on its hexagon head or nut. A finer pitch of 1 mm or 0.75 mm exists, but it is only fitted to some products. Simfix stocks M8 hexagon head set screws in A2 and A4 stainless steel.
What spanner fits an M10 bolt?
An M10 hexagon head bolt to ISO 4017 or ISO 4014 takes a 16 mm spanner. Older DIN 933 and DIN 934 parts use 17 mm, because ISO 272 changed M10 from 17 mm to 16 mm in 1982. For DIN 933 M10, check the product page or email contact@simfix.com for the head size.
What Allen key fits an M6 socket cap screw?
An M6 socket cap screw to ISO 4762 takes a 5 mm hex key. The key size is the width across the flats of the hexagon socket. Other sizes are M4 with 3 mm, M5 with 4 mm, M8 with 6 mm and M10 with 8 mm. Simfix stocks M6 socket cap screws in A2 and A4.
What drill size do I use to tap an M8 thread?
Drill a 6.8 mm hole to tap an M8 coarse thread, which has a 1.25 mm pitch. For M6 the tap drill is 5 mm, for M10 it is 8.5 mm and for M12 it is 10.2 mm. The full list for M3 to M24, with UNC, UNF and BSW sizes, is on the tap drill size chart.
What is the pitch of an M10 bolt?
An M10 bolt has a coarse thread pitch of 1.5 mm. This is the standard pitch for M10 in ISO 262. Fine pitches of 1.25 mm and 1 mm also exist for M10, and a few Simfix products list them. M10 bolts to ISO 4017 and DIN 933 are stocked in A2 and A4 stainless steel.
Which bolt sizes does Simfix stock in stainless steel?
Simfix stocks fully threaded ISO 4017 hexagon head set screws in A2 (304) from M2 to M39 and in A4 (316) from M2.5 to M42. Part threaded hexagon head bolts (ISO 4014 and DIN 931) run from M5 to M45 in A2 and M5 to M48 in A4. Not every length is held in every size.
See also: Fastener size guide, Tap drill size chart, Stainless steel bolt torque chart and the stainless steel fastener glossary.