M4 vs M6
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.
| M4 | M6 | |
|---|---|---|
| Thread diameter | 4.00 mm | 6.00 mm |
| Standard pitch | 0.7 mm | 1 mm |
| Tap drill | 3.3 mm | 5 mm |
| Clearance hole | 4.5 mm | 6.6 mm |
| Cap head Ø | 7 mm | 10 mm |
| Hex key | 3.0 mm | 5.0 mm |
| Torque into steel | 2.0-3.0 N·m | 7-10 N·m |
| Into plastic | 0.8-1.4 N·m | 2.5-4.0 N·m |
M4 is normally used for
Rack panels and cage nuts, monitors, VESA 75/100 plates, machine covers, e-bike parts
Everything M4 fits →M6 is normally used for
VESA 200 mounts, bike brake calipers, machine frames, heavy enclosures, furniture
Everything M6 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 — 4.0 mm means M4, 6.0 mm means M6.
Use the screw size finder →Buy either size
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M4 screws
Assorted lengths in one box
M6 screws
Assorted lengths in one box
Digital caliper
Tells the two sizes apart for certain