Reference sheet
Screws & standoffs
M2 / M2.5 / M3 sizes and the mounting holes on common boards
Screws & standoffs
Metric screw sizes are named by their thread diameter, so an M3 screw needs a ~3.2 mm clearance hole (or a 2.5 mm hole to cut its own thread in plastic). Nylon standoffs are the safe default over a PCB — brass ones short anything they touch.
| Size | Thread ⌀ | Clearance hole | Head ⌀ (pan, ISO 7045) | Pitch | Seen on |
|---|---|---|---|---|---|
| M2 | 2.0 mm | 2.2–2.4 mm | 4.0 mm | 0.4 mm | Small sensor and camera modules, ESP32-CAM |
| M2.5 | 2.5 mm | 2.7–2.9 mm | 5.0 mm | 0.45 mm | Raspberry Pi and most SBC mounting holes |
| M3 | 3.0 mm | 3.2–3.4 mm | 5.5 mm | 0.5 mm | Arduino Uno/Mega, enclosures, the maker default |
| M4 | 4.0 mm | 4.3–4.5 mm | 8.0 mm | 0.7 mm | Panel mounting, heatsinks, motor brackets |
| #4-40 (imperial) | 2.84 mm | 3.1 mm | 5.5 mm | 40 TPI | US enclosures and standoffs — NOT interchangeable with M3 |
| Board | Mounting holes | Screw |
|---|---|---|
| Arduino Uno / Leonardo | 4 holes, 3.2 mm | M3 |
| Arduino Mega 2560 | 6 holes, 3.2 mm (the Uno four, plus two at the long end) | M3 |
| Raspberry Pi (all 40-pin models) | 4 holes, 2.75 mm, 58 × 49 mm apart | M2.5 |
| Raspberry Pi Pico | 4 holes, 2.1 mm | M2 |
| ESP32 DevKit / NodeMCU | usually none — hold it by the header | — |
| ESP32-CAM | 2 holes, 2.1 mm | M2 |
