M3 Metric Thread
Direct Answer
M3 is an ISO metric machine screw thread with a nominal major diameter of 3.0 mm and a standard coarse pitch of 0.50 mm. Requiring a 2.50 mm tap drill, it is the world's most widely deployed fastener in 3D printers, consumer electronics, and PC 5.25-inch optical drive bays.
Source: ISO 68-1 / ISO 261 / DIN 13-1
Specs
| Nominal Major Diameter | 3.00 mm |
| Standard Coarse Pitch | 0.50 mm |
| Fine Pitch (Optional) | 0.35 mm |
| Tap Drill Diameter | 2.50 mm (75% thread engagement) |
| Minor Diameter (Internal) | 2.459 mm |
| Tensile Stress Area | 5.03 mm² |
| Common Drive Size | PH1 / PH2 / 2.5mm Hex / T10 |
3D Printing and DIY Maker Standard
M3 socket head cap screws (DIN 912) and M3 heat-set brass threaded inserts (M3×4mm/5mm) are the universal mechanical standard across open-source 3D printers (Prusa, Voron, Bambu Lab) and DIY robotics assemblies.
PC Optical Drives vs Motherboard Standoffs
In PC cases, M3 screws are used exclusively for optical drives (5.25-inch bays) and 2.5-inch SSD adapters. While some motherboard standoffs use M3 internal threads, others use #6-32 UNC; forcing a #6-32 screw into an M3 standoff will bind and cross-thread immediately.