M3 vs #4-40 UNC Screw Size Chart
Overview
Technical specifications for M3 metric and #4-40 UNC imperial fasteners. These small sizes are frequently used in precision assemblies and electronics.
Comparison Table
| Standard | Size | Diameter (mm) | Pitch / TPI | Tap Drill |
|---|---|---|---|---|
| Metric | M3 | 3.00 mm | 0.50 mm | 2.5 mm |
| Imperial | #4-40 UNC | 2.84 mm | 40 TPI | 2.25 mm (#43) |
FAQ
Is M3 the same as #4-40?
No. An M3 bolt (3.00 mm) is physically larger than a #4-40 bolt (2.84 mm). While they look similar to the naked eye, the thread pitches are entirely different (0.50mm vs 0.64mm pitch equivalent).
Source Standard
ISO 261 / ANSI B1.1