Technically reviewed by Vincent, Founder at HEXVARO
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Quick answer
Quick answer: common clearance holes
For M6, M8, M10 and M12 bolts, the medium series holes are 6.6, 9, 11 and 13.5 mm. Use the fine series when several bolts must locate a part accurately, and the coarse series when you need room for alignment.
| Size | Fine (mm) | Medium (mm) | Coarse (mm) | Inquiry |
|---|---|---|---|---|
| M6 | 6.4 | 6.6 | 7.0 | Quote this size |
| M8 | 8.4 | 9.0 | 10.0 | Quote this size |
| M10 | 10.5 | 11.0 | 12.0 | Quote this size |
| M12 | 13.0 | 13.5 | 14.5 | Quote this size |
| M16 | 17.0 | 17.5 | 18.5 | Quote this size |
| M20 | 21.0 | 22.0 | 24.0 | Quote this size |
Sourcing these sizes? DIN 933 full-thread hex bolts Industrial washer supplier
ISO 273 clearance hole chart (mm)
Fine is often called close fit, medium normal fit and coarse loose fit. Hole tolerances are usually H12 for fine, H13 for medium and H14 for coarse. Some older company charts round M12 and above differently, so follow the drawing where it differs.
| Size | Fine / close (mm) | Medium / normal (mm) | Coarse / loose (mm) | Inquiry |
|---|---|---|---|---|
| M3 | 3.2 | 3.4 | 3.6 | Quote this size |
| M4 | 4.3 | 4.5 | 4.8 | Quote this size |
| M5 | 5.3 | 5.5 | 5.8 | Quote this size |
| M6 | 6.4 | 6.6 | 7.0 | Quote this size |
| M8 | 8.4 | 9.0 | 10.0 | Quote this size |
| M10 | 10.5 | 11.0 | 12.0 | Quote this size |
| M12 | 13.0 | 13.5 | 14.5 | Quote this size |
| M14 | 15.0 | 15.5 | 16.5 | Quote this size |
| M16 | 17.0 | 17.5 | 18.5 | Quote this size |
| M18 | 19.0 | 20.0 | 21.0 | Quote this size |
| M20 | 21.0 | 22.0 | 24.0 | Quote this size |
| M22 | 23.0 | 24.0 | 26.0 | Quote this size |
| M24 | 25.0 | 26.0 | 28.0 | Quote this size |
| M27 | 28.0 | 30.0 | 32.0 | Quote this size |
| M30 | 31.0 | 33.0 | 35.0 | Quote this size |
| M33 | 34.0 | 36.0 | 38.0 | Quote this size |
| M36 | 37.0 | 39.0 | 42.0 | Quote this size |
Clearance hole and tap drill together
A clearance hole lets the bolt pass through. A tap drill hole is smaller and is threaded afterwards. Mixing them up is a common drawing error, so this table shows both for coarse thread.
| Size | Thread pitch (mm) | Tap drill (mm) | Medium clearance (mm) | Inquiry |
|---|---|---|---|---|
| M3 | 0.5 | 2.5 | 3.4 | Quote this size |
| M4 | 0.7 | 3.3 | 4.5 | Quote this size |
| M5 | 0.8 | 4.2 | 5.5 | Quote this size |
| M6 | 1.0 | 5.0 | 6.6 | Quote this size |
| M8 | 1.25 | 6.8 | 9.0 | Quote this size |
| M10 | 1.5 | 8.5 | 11.0 | Quote this size |
| M12 | 1.75 | 10.2 | 13.5 | Quote this size |
| M14 | 2.0 | 12.0 | 15.5 | Quote this size |
| M16 | 2.0 | 14.0 | 17.5 | Quote this size |
| M18 | 2.5 | 15.5 | 20.0 | Quote this size |
| M20 | 2.5 | 17.5 | 22.0 | Quote this size |
| M22 | 2.5 | 19.5 | 24.0 | Quote this size |
| M24 | 3.0 | 21.0 | 26.0 | Quote this size |
| M27 | 3.0 | 24.0 | 30.0 | Quote this size |
| M30 | 3.5 | 26.5 | 33.0 | Quote this size |
| M33 | 3.5 | 29.5 | 36.0 | Quote this size |
| M36 | 4.0 | 32.0 | 39.0 | Quote this size |
How to choose fine, medium or coarse
- Fine: dowel-free location where parts must line up closely, and where the hole position is accurate.
- Medium: general machine building and steel fabrication. Use this unless you have a reason not to.
- Coarse: site assembly, slotted frames, and parts that need room for alignment.
- Coated bolts: allow for coating thickness. Hot-dip galvanized bolts and galvanized holes both lose clearance.
Check the head and washer as well
A larger hole reduces the bearing area under the bolt head. If the hole is coarse or the material is soft, add a flat washer. Check that the washer's outside diameter still sits on solid material. For structural steelwork, hole sizes come from the project standard rather than ISO 273.
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.
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- MOQ: 500 pcs per specification
- Lead time: 10–15 days stock items
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- Experience: Founder with 10+ years in the fastener industry
Frequently asked questions
What size clearance hole for an M6 bolt?
6.6 mm in the medium series. The fine series is 6.4 mm and the coarse series is 7.0 mm.
What size clearance hole for an M8 bolt?
9.0 mm in the medium series. The fine series is 8.4 mm and the coarse series is 10.0 mm.
What size clearance hole for an M10 bolt?
11.0 mm in the medium series. The fine series is 10.5 mm and the coarse series is 12.0 mm.
What size clearance hole for an M12 bolt?
13.5 mm in the medium series. The fine series is 13.0 mm and the coarse series is 14.5 mm.
What size clearance hole for an M16 bolt?
17.5 mm in the medium series. The fine series is 17.0 mm and the coarse series is 18.5 mm.
What is the difference between a clearance hole and a tap drill hole?
A clearance hole is larger than the bolt, so the bolt passes through. A tap drill hole is smaller than the bolt, so a thread can be cut into it.
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