---
type: "drill"
designation: "10.8 mm"
series: "metric"
series_name: "Metric Drill Sizes"
diameter_in: 0.425197
diameter_mm: 10.8
standard: "ANSI/ASME B94.11M; BS 328"
verified: "August 1, 2026"
url: https://shopmath.org/drills/metric/10-8mm
---

# 10.8 mm Drill Bit Size — 0.4252 in / 10.800 mm

A 10.8 mm drill bit is 0.4252 in (10.800 mm) in diameter. It belongs to the metric series of standard twist drills. It is the recommended tap drill for M12×1.25.

- **Designation**: 10.8 mm
- **Series**: Metric
- **Diameter**: 0.4252 in (10.800 mm)

## 10.8 mm Drill Diameter

| Property | Value |
| --- | --- |
| Designation | 10.8 mm |
| Series | Metric |
| Diameter (in) | 0.4252 |
| Diameter (mm) | 10.800 |

## 10.8 mm Drill Equivalents in the Other Size Series

The nearest standard drill to 10.8 mm in each of the other three series. Nothing here is an exact match unless the difference column reads 0.0000 in.

| Series | Nearest drill | Diameter (in) | Diameter (mm) | Difference |
| --- | --- | --- | --- | --- |
| Number | [#1](https://shopmath.org/drills/number/1.md) | 0.2280 | 5.791 | -0.1972 in |
| Letter | [Z](https://shopmath.org/drills/letter/z.md) | 0.4130 | 10.490 | -0.0122 in |
| Fractional | [27/64](https://shopmath.org/drills/fractional/27-64.md) | 0.4219 | 10.716 | -0.0033 in |

## Threads Tapped With a 10.8 mm Drill

| Thread | Pitch | Thread engagement (%) |
| --- | --- | --- |
| [M12×1.25](https://shopmath.org/threads/metric-fine/m12x1.25.md) | 1.250 mm | 73.9 |

_Engagement is what the real drill leaves with a cut tap, not the requested target._

## Sources and Method for the 10.8 mm Drill Size

### Drill index

- **Source**: Number/letter: bd_warehouse drill_sizes.csv (Apache-2.0) cross-checked against Wikipedia Drill bit sizes (CC BY-SA 4.0). Fractional: computed 1/64 in steps per ANSI B94.11M. Metric: computed BS 328 increment pattern.
- **Method**: computed
- **Verified against**: Wikipedia Drill bit sizes (CC BY-SA 4.0); 31/31 checks passed

### Assumptions

- Drill diameters are nominal. A worn or run-out drill cuts oversize; measure the hole, not the shank, when the fit matters.
- Dataset scope: Number sizes #61-#80 are stored but tagged demandTier 'extended' — query-space-map.md Appendix A found the tail thinning in the 60s. Sizes below #80 and metric sizes above 25.0 mm excluded.

**Data last verified**: August 1, 2026

## Common Questions About the 10.8 mm Drill Bit

### What size is a 10.8 mm drill bit size?

A 10.8 mm drill bit is 0.4252 in (10.800 mm) in diameter.

### What fraction is a 10.8 mm drill bit?

10.8 mm is 0.4252 in (10.800 mm), which is not itself a fractional size. The closest fractional drill is 27/64 at 0.4219 in (10.716 mm).

### What thread does a 10.8 mm drill bit tap?

A 10.8 mm drill is the recommended tap drill for M12×1.25. That leaves the thread engagement shown in the table above with a cut tap.

## Related pages

- Next size down (any series): [27/64](https://shopmath.org/drills/fractional/27-64.md) — 0.4219 in (10.716 mm)
- Next size up (any series): [10.9 mm](https://shopmath.org/drills/metric/10-9mm.md) — 0.4291 in (10.900 mm)
- Previous in the metric series: [10.7 mm](https://shopmath.org/drills/metric/10-7mm.md)
- Next in the metric series: [10.9 mm](https://shopmath.org/drills/metric/10-9mm.md)
- All metric sizes: [Metric drill sizes](https://shopmath.org/drills/metric.md)
- All drill sizes: [Drill bit size reference](https://shopmath.org/drills.md)
- Complete index by diameter: [Drill size chart](https://shopmath.org/charts/drill-sizes.md)
- Tap drills by thread: [Tap drill chart](https://shopmath.org/charts/tap-drill.md)

---

*Source: [ShopMath](https://shopmath.org/drills/metric/10-8mm) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*