M2.5 vs M3
They differ by 0.5 mm across the threads — enough that they are never interchangeable, but little enough that they are easy to mix up in a parts tray.
| M2.5 | M3 | |
|---|---|---|
| Thread diameter | 2.50 mm | 3.00 mm |
| Standard pitch | 0.45 mm | 0.5 mm |
| Tap drill | 2.05 mm | 2.5 mm |
| Clearance hole | 2.9 mm | 3.4 mm |
| Cap head Ø | 4.5 mm | 5.5 mm |
| Hex key | 2.0 mm | 2.5 mm |
| Torque into steel | 45-70 N·cm | 80-130 N·cm |
| Into plastic | 20-35 N·cm | 35-60 N·cm |
M2.5 is normally used for
The classic laptop bottom-case screw, hard drive cages, Raspberry Pi mounting holes
Everything M2.5 fits →M3 is normally used for
PC cases, 2.5in drives, 3D printers, extrusion hardware, DIN-rail devices, robotics
Everything M3 fits →If you are not sure which one you have
Measure across the outside of the threads with a caliper. A reading within about 0.1 mm of the nominal size is your answer — 2.5 mm means M2.5, 3.0 mm means M3.
Use the screw size finder →Buy either size
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M2.5 screws
Assorted lengths in one box
M3 screws
Assorted lengths in one box
Digital caliper
Tells the two sizes apart for certain