These three sizes cover most screws inside laptops, SSDs, single-board computers and small electronics, and they get mixed up constantly. Here are the real dimensions side by side, from the ISO standards.
M2 vs M2.5 vs M3 dimension chart
| M2 | M2.5 | M3 | |
|---|---|---|---|
| Thread outside diameter | 2.0mm | 2.5mm | 3.0mm |
| Coarse pitch (ISO 261) | 0.4mm | 0.45mm | 0.5mm |
| Tap drill | 1.6mm | 2.05mm | 2.5mm |
| Clearance hole, close / medium (ISO 273) | 2.2 / 2.4mm | 2.7 / 2.9mm | 3.2 / 3.4mm |
| Flat (countersunk) head diameter, ISO 7046 | 3.8mm | 4.7mm | 5.5mm |
| Pan head diameter, ISO 7045 | 4.0mm | 5.0mm | 5.6mm |
| Phillips driver (ISO 7045 / 7046) | PH0 | PH1 | PH1 |
| Lengths in stock here | 2mm, 3mm, 4mm, 5mm, 6mm, 8mm | 3mm, 4mm, 5mm, 6mm, 8mm, 10mm, 12mm, 14mm | 3mm, 4mm, 5mm, 6mm, 8mm, 10mm, 12mm, 14mm |
Head diameters are the ISO maximums for standard machine screws. Laptop screws often have thinner, non-standard "wafer" heads, so compare the head with your original screw as well.
How to identify your screw
- Diameter: measure across the threads. 2.0, 2.5 or 3.0mm (screws read a little under nominal).
- Length: flat heads from the top of the head to the tip; pan heads from under the head to the tip.
- Head: flat (countersunk, sits flush) or pan (domed, sits on top).
- Cross-check: it should thread in by hand for two or three turns. If it binds straight away, it is the wrong size; stop before you strip the hole.
Typical uses
| Size | Common in | Example in stock | All sizes |
|---|---|---|---|
| M2 | M.2 SSDs, laptop internals, keyboards | M2 x 4mm Phillips Flat Head Machine Screws Black 50-Pack Electronics Repair Kit | M2 screws |
| M2.5 | Laptop bottom covers and motherboards, Raspberry Pi | M2.5 x 6mm Laptop Motherboard Replacement Screws Flat Head 10-Pack Black | M2.5 screws |
| M3 | 2.5" SSDs and hard drives, brackets | M3 x 4mm Phillips Flat Head Screws for 2.5 SATA SSD Mounting 10-Pack | M3 screws |
More detail: M2 screw guide, M3 screw guide, Raspberry Pi screw size, hard drive screw sizes.
FAQ
What is the difference between M2 and M2.5 screws?
Half a millimetre of thread diameter: M2 is 2.0mm across the threads with a 0.4mm pitch, M2.5 is 2.5mm with a 0.45mm pitch. They do not interchange: an M2 spins loose in an M2.5 hole and an M2.5 will not start in an M2 hole.
What does M2.5 mean on a screw?
M = ISO metric thread, 2.5 = the nominal outside diameter of the thread in millimetres. "M2.5 x 6" adds the length: 6mm, measured from under the head for pan heads and from the top of the head for flat (countersunk) heads.
How can I tell M2, M2.5 and M3 apart without calipers?
Compare against a known screw or drill bits: a 2mm bit matches M2 threads, 2.5mm matches M2.5, 3mm matches M3. Calipers across the threads read about 1.9-2.0, 2.4-2.5 and 2.9-3.0mm.
Is M2.5 the same as M2.6?
No. M2.6 is a JIS size some Japanese electronics still use. It has the same 0.45mm pitch but is 0.1mm larger, so an M2.5 screw is loose in an M2.6 hole and an M2.6 screw forces an M2.5 hole. Use the size the hole was made for.
Where are M2, M2.5 and M3 used?
M2: M.2 SSDs and many small laptop internals. M2.5: laptop bottom covers and motherboards, Raspberry Pi boards. M3: 2.5" SSDs and hard drives, and many small brackets.