M4 vs #8-32 UNC Screw Size Comparison
Overview
Technical dimensional reference for M4 metric and #8-32 UNC imperial screws. These are close in size but are not functionally interchangeable.
Comparison Table
| Standard | Size | Diameter (mm) | Pitch / TPI | Tap Drill |
|---|---|---|---|---|
| Metric | M4 | 4.00 mm | 0.70 mm | 3.3 mm |
| Imperial | #8-32 UNC | 4.17 mm | 32 TPI | 3.5 mm (#29) |
FAQ
Can I use M4 instead of #8-32?
No. An M4 screw (4.00 mm) is slightly smaller than a #8-32 screw (4.17 mm). Additionally, the thread pitch for M4 is 0.70 mm, while #8-32 is approximately 0.79 mm, making them incompatible.
Source Standard
ISO 261 / ANSI B1.1