Drilling & Fabrication
8 mm drill bit size
Quick reference for 8 mm drill bits: exact decimal inches and nearest fractional equivalents for common workshop denominators. Includes practical guidance and related charts.
Nearest fractional sizes
- 1/16 increments: 5/16" (approx)
- 1/32 increments: 5/16" (near‑match)
- 1/64 increments: 5/16" (closest among common denominators)
Use fractional equivalents when tooling or documentation requires imperial sizes. Always check tolerance demands before substituting fractional bits.
Practical guidance
- Use sharp HSS or carbide bits; mark with a center punch.
- High RPM, light feed; reduce pressure at breakthrough.
- Support exit side; use cutting fluid for metals.
- Deburr lightly; verify hole size with calipers if tolerance matters.
Clearance & tapping coverage
Approximate coarse‑pitch coverage for metric threads near this bit. Tap drill is approximated by (major − pitch). Clearance values vary by fit class; use manufacturer tables and ISO references for production.
| Thread | Pitch (mm) | Tap drill (mm) | Clearance close / std / loose (mm) | Bit relation |
|---|---|---|---|---|
| M8 | 1.25 | 6.75 | 8.20 / 8.40 / 8.60 | near |
| M9 | 1.25 | 7.75 | 9.20 / 9.40 / 9.60 | near |
| M7 | 1.00 | 6.00 | 7.20 / 7.40 / 7.60 | near |
| M10 | 1.50 | 8.50 | 10.20 / 10.40 / 10.60 | near |
| M6 | 1.00 | 5.00 | 6.20 / 6.40 / 6.60 | near |
| M11 | 1.50 | 9.50 | 11.20 / 11.40 / 11.60 | near |
| M12 | 1.75 | 10.25 | 12.20 / 12.40 / 12.60 | near |
| M5 | 0.80 | 4.20 | 5.20 / 5.40 / 5.60 | near |
FAQ
What is a 8 mm drill bit in inches?
8 mm equals 0.31496 inches. Nearest fractional sizes are 5/16" and 5/16". Choose the fraction that best fits your tolerance and material.
What is 8 mm used for?
Common applications include pilot holes for small fasteners, plastics and soft woods, thin sheet metal, model making, and electronics enclosures. Use high RPM with light feed, and support workpieces to avoid burrs.
How do I avoid tear‑out with a 8 mm bit?
Mark with a center punch, use sharp bits, reduce feed near breakthrough, and support the exit side with scrap backing. For metals, use cutting fluid and keep chips clear.
Need more tooling references?
Compare full drill bit tables, review tap drill recommendations, or switch to the mm→in calculator for arbitrary sizes. Printable charts are available.