# Imperial machine screws: #4-40, #6-32, #8-32, 1/4-20

> What are the clearance and tap drill sizes for #4-40, #6-32, #8-32 and 1/4-20?

- Category: Hardware › Fasteners
- Kind: Hardware
- Basis: ASME B18.6.3 / B18.3; Unified thread standard
- Page: https://xemstudio.com/objects/imperial-machine-screws/ · JSON: https://xemstudio.com/api/geometry?object=imperial-machine-screws · Plain text: https://xemstudio.com/objects/imperial-machine-screws/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

## Notes

- Major diameters: #4 2.845 mm (0.112 in), #6 3.505 mm (0.138 in), #8 4.166 mm (0.164 in), 1/4 6.35 mm.
- Socket head: head dia ≈ 1.5 × major, head height = major. 1/4-20 SHCS: 0.375 in head, 0.25 in tall, 3/16 in hex key.

## Sizes

| size | major_mm | tpi | clearance_mm | tap_drill_mm |
|---|---|---|---|---|
| #4-40 | 2.845 | 40 | 3.3 | 2.26 |
| #6-32 | 3.505 | 32 | 3.9 | 2.7 |
| #8-32 | 4.166 | 32 | 4.5 | 3.45 |
| 1/4-20 | 6.35 | 20 | 6.8 | 5.11 |

## Where the files are

- McMaster-Carr: [Machine screws (free STEP/IGES/STL per part, for your own design use; no redistribution)](https://www.mcmaster.com/products/screws/machine-screws/) — STEP, IGES, STL, PDF — McMaster-Carr site terms: personal design use, no redistribution (verify at link)
- Wikipedia: [Unified Thread Standard](https://en.wikipedia.org/wiki/Unified_Thread_Standard) — web — CC BY-SA 4.0 (text)

## Free STEP/STL (18 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/imperial-machine-screws/index.json

- shcs-4-40x6.35mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-4-40x6.35mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-4-40x6.35mm.stl) — #4-40 SHCS × 6.35 mm, thread as plain cylinder
- shcs-4-40x9.5mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-4-40x9.5mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-4-40x9.5mm.stl) — #4-40 SHCS × 9.5 mm, thread as plain cylinder
- shcs-4-40x12.7mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-4-40x12.7mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-4-40x12.7mm.stl) — #4-40 SHCS × 12.7 mm, thread as plain cylinder
- shcs-4-40x19mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-4-40x19mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-4-40x19mm.stl) — #4-40 SHCS × 19 mm, thread as plain cylinder
- shcs-6-32x6.35mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-6-32x6.35mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-6-32x6.35mm.stl) — #6-32 SHCS × 6.35 mm, thread as plain cylinder
- shcs-6-32x9.5mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-6-32x9.5mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-6-32x9.5mm.stl) — #6-32 SHCS × 9.5 mm, thread as plain cylinder
- shcs-6-32x12.7mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-6-32x12.7mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-6-32x12.7mm.stl) — #6-32 SHCS × 12.7 mm, thread as plain cylinder
- shcs-6-32x19mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-6-32x19mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-6-32x19mm.stl) — #6-32 SHCS × 19 mm, thread as plain cylinder
- shcs-6-32x25.4mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-6-32x25.4mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-6-32x25.4mm.stl) — #6-32 SHCS × 25.4 mm, thread as plain cylinder
- shcs-8-32x9.5mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-8-32x9.5mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-8-32x9.5mm.stl) — #8-32 SHCS × 9.5 mm, thread as plain cylinder
- shcs-8-32x12.7mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-8-32x12.7mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-8-32x12.7mm.stl) — #8-32 SHCS × 12.7 mm, thread as plain cylinder
- shcs-8-32x19mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-8-32x19mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-8-32x19mm.stl) — #8-32 SHCS × 19 mm, thread as plain cylinder
- shcs-8-32x25.4mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-8-32x25.4mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-8-32x25.4mm.stl) — #8-32 SHCS × 25.4 mm, thread as plain cylinder
- shcs-1-4-20x12.7mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-1-4-20x12.7mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-1-4-20x12.7mm.stl) — #1-4-20 SHCS × 12.7 mm, thread as plain cylinder
- shcs-1-4-20x19mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-1-4-20x19mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-1-4-20x19mm.stl) — #1-4-20 SHCS × 19 mm, thread as plain cylinder
- shcs-1-4-20x25.4mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-1-4-20x25.4mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-1-4-20x25.4mm.stl) — #1-4-20 SHCS × 25.4 mm, thread as plain cylinder
- shcs-1-4-20x31.75mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-1-4-20x31.75mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-1-4-20x31.75mm.stl) — #1-4-20 SHCS × 31.75 mm, thread as plain cylinder
- shcs-1-4-20x38.1mm: [STEP](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-1-4-20x38.1mm.step) · [STL](https://xemstudio.com/files/hardware/imperial-machine-screws/shcs-1-4-20x38.1mm.stl) — #1-4-20 SHCS × 38.1 mm, thread as plain cylinder

## Questions

**What is the diameter of a #4-40, #6-32 and #8-32 screw in mm?**

#4-40: 2.845 mm (0.112 in). #6-32: 3.505 mm (0.138 in). #8-32: 4.166 mm (0.164 in). 1/4-20: 6.35 mm.

**What is the clearance hole for a #6-32 screw?**

3.9 mm (0.1495 in, #25 drill); tap drill 2.7 mm (#36). #4-40: clearance 3.3 mm, tap 2.26 mm (#43). #8-32: clearance 4.5 mm, tap 3.45 mm (#29).

**Is #6-32 the same as M3.5?**

Close but not interchangeable: #6-32 is 3.505 mm with 32 TPI (0.794 mm pitch); M3.5 is 3.5 mm with a 0.6 mm pitch. Use metric nuts on metric screws.

## Fits with

- [Socket head cap screws, M2–M8 (ISO 4762 / DIN 912)](https://xemstudio.com/objects/socket-head-cap-screws-metric/)
- [Schedule 40 pipe and PVC fittings, 1/2 to 2 inch](https://xemstudio.com/objects/schedule-40-pipe/)