---
type: "drill"
designation: "5.1 mm"
series: "metric"
series_name: "Metric Drill Sizes"
diameter_in: 0.200787
diameter_mm: 5.1
standard: "ANSI/ASME B94.11M; BS 328"
verified: "August 1, 2026"
url: https://shopmath.org/drills/metric/5-1mm
---

# 5.1 mm Drill Bit Size — 0.2008 in / 5.100 mm

A 5.1 mm drill bit is 0.2008 in (5.100 mm) in diameter. It belongs to the metric series of standard twist drills.

- **Designation**: 5.1 mm
- **Series**: Metric
- **Diameter**: 0.2008 in (5.100 mm)

## 5.1 mm Drill Diameter

| Property | Value |
| --- | --- |
| Designation | 5.1 mm |
| Series | Metric |
| Diameter (in) | 0.2008 |
| Diameter (mm) | 5.100 |

## 5.1 mm Drill Equivalents in the Other Size Series

The nearest standard drill to 5.1 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 | [#7](https://shopmath.org/drills/number/7.md) | 0.2010 | 5.105 | +0.0002 in |
| Letter | [A](https://shopmath.org/drills/letter/a.md) | 0.2340 | 5.944 | +0.0332 in |
| Fractional | [13/64](https://shopmath.org/drills/fractional/13-64.md) | 0.2031 | 5.159 | +0.0023 in |

## Sources and Method for the 5.1 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 5.1 mm Drill Bit

### What size is a 5.1 mm drill bit size?

A 5.1 mm drill bit is 0.2008 in (5.100 mm) in diameter.

### What fraction is a 5.1 mm drill bit?

5.1 mm is 0.2008 in (5.100 mm), which is not itself a fractional size. The closest fractional drill is 13/64 at 0.2031 in (5.159 mm).

## Related pages

- Next size down (any series): [#8](https://shopmath.org/drills/number/8.md) — 0.1990 in (5.055 mm)
- Next size up (any series): [#7](https://shopmath.org/drills/number/7.md) — 0.2010 in (5.105 mm)
- Previous in the metric series: [5 mm](https://shopmath.org/drills/metric/5mm.md)
- Next in the metric series: [5.2 mm](https://shopmath.org/drills/metric/5-2mm.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/5-1mm) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*