M3 vs M5
They differ by 2.0 mm across the threads — enough that they are never interchangeable, but little enough that they are easy to mix up in a parts tray.
| M3 | M5 | |
|---|---|---|
| Thread diameter | 3.00 mm | 5.00 mm |
| Standard pitch | 0.5 mm | 0.8 mm |
| Tap drill | 2.5 mm | 4.2 mm |
| Clearance hole | 3.4 mm | 5.5 mm |
| Cap head Ø | 5.5 mm | 8.5 mm |
| Hex key | 2.5 mm | 4.0 mm |
| Torque into steel | 80-130 N·cm | 4.0-6.0 N·m |
| Into plastic | 35-60 N·cm | 1.5-2.5 N·m |
M3 is normally used for
PC cases, 2.5in drives, 3D printers, extrusion hardware, DIN-rail devices, robotics
Everything M3 fits →M5 is normally used for
VESA 100 monitor mounts, bike bottle cages and disc rotors, rack rails, appliance panels
Everything M5 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 — 3.0 mm means M3, 5.0 mm means M5.
Use the screw size finder →Buy either size
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M3 screws
Assorted lengths in one box
M5 screws
Assorted lengths in one box
Digital caliper
Tells the two sizes apart for certain