When replacing missing hardware or shopping for fasteners, guessing screw sizes often leads to stripped threads or wasted trips to the hardware store. Here is how to identify any fastener using an on-screen millimeter scale.
Anatomy: Diameter vs. Length vs. Pitch
Every threaded fastener is defined by three fundamental dimensions:
- Major Diameter: The thickness across the widest outer ridges of the threads.
- Length: The depth of the screw that actually enters the workpiece.
- Thread Pitch: The distance between individual crests (e.g. 0.8 mm pitch on M5).
How to Measure Thread Diameter on Screen
Place the screw directly on your phone or laptop display using our Millimeters Ruler. Turn on the interactive Crosshair Guides in the toolbar to lock crosshair lines onto both sides of the threaded shank.
Metric Screw Diameter Chart (M2 to M10)
| Metric Size | Major Diameter (mm) | Equivalent Inches | Standard Coarse Pitch |
|---|---|---|---|
| M2 | 2.0 mm | 0.0787″ | 0.40 mm |
| M3 | 3.0 mm | 0.1181″ | 0.50 mm |
| M4 | 4.0 mm | 0.1575″ | 0.70 mm |
| M5 | 5.0 mm | 0.1969″ | 0.80 mm |
| M6 | 6.0 mm | 0.2362″ | 1.00 mm |
| M8 | 8.0 mm | 0.3150″ | 1.25 mm |
