Verified by Rachel Mayfield, Supply Chain Analyst - August 2026
An M2.5 screw has a 2.5 mm thread diameter with a 0.45 mm coarse pitch, and the head size depends on the head type: the pan head measures 5 mm across, the countersunk head 4.7 mm, and the socket cap 4.5 mm. Drill 2.05 mm to tap an M2.5 thread and 2.9 mm for a standard clearance hole. The tables below give every head type with its standard, plus the drill sizes, and flag where DIN and ISO figures quietly differ.
M2.5 screw head dimensions by head type
| Head type | Standard | Head diameter (max) | Head height (max) | Drive |
|---|
| Pan head | ISO 7045 | 5 mm | 2.1 mm | Cross recess No. 1 (PH1 or PZ1 driver) |
| Countersunk | ISO 7046-1 | 4.7 mm | 1.5 mm | Cross recess No. 1 (PH1 or PZ1 driver) |
| Socket cap | ISO 4762 / DIN 912 | 4.5 mm | 2.5 mm | 2 mm hex key |
| Cheese head (slotted) | DIN 84 | 4.5 mm | 1.6 mm | 0.6 mm slot |
There is no M2.5 row in the button head standard - ISO 7380-1 starts at M3. Below that, pan or cheese heads do the job a button head would.
M2.5 thread, tapping and clearance sizes
| Property | Value | Standard |
|---|
| Thread diameter | 2.5 mm nominal | ISO 261 |
| Coarse pitch | 0.45 mm | ISO 261 |
| Fine pitch (thread only, see note) | 0.35 mm | ISO 261 |
| Tapping drill (coarse, 75% engagement) | 2.05 mm | = diameter minus pitch |
| Clearance hole - close fit | 2.7 mm (H12) | ISO 273 fine series |
| Clearance hole - medium fit | 2.9 mm (H13) | ISO 273 medium series |
| Clearance hole - coarse fit | 3.1 mm (H14) | ISO 273 coarse series |
The fine pitch exists for the M2.5 thread but not in the machine screw standards - ISO 7045 and ISO 7046-1 are coarse pitch only, so a fine-pitch M2.5 is a bolt, cap screw or studding question. Tapping drill is diameter minus pitch, which gives roughly 75% thread engagement; going undersize makes small taps snap without adding useful strength.
DIN and ISO head sizes are not identical on M2.5
Suppliers list DIN 7985/ISO 7045 and DIN 965/ISO 7046 as equivalents. The thread is identical, the heads are not always. On the pan head, DIN 7985 gives a head height 2.0 mm (vs 2.1 mm in ISO 7045). Mixed batches look wrong on an assembly and can foul recessed fixing holes, so state the standard on the drawing, not just the size.
Is an M2.5 screw the same as an M2.5 bolt?
The thread is identical: M2.5 x 0.45 mm coarse to ISO 261. In practice M2.5 is screw territory - hex-head bolts in this diameter are uncommon, and the socket cap screw in the table above is what drawings call up when a stronger fastener is needed. Machine screws to ISO 7045 and ISO 7046-1 are property class 4.8 steel or A2/A4 stainless; socket caps to ISO 4762 come in 8.8, 10.9 and 12.9.
Where M2.5 screws turn up
M2.5 screws are the usual fixing in laptop internals, Raspberry Pi and PCB mounting, and small instrument assemblies. Pan heads suit anything where the head sits on the surface, countersunk heads need a chamfered hole to finish flush, and the socket cap takes over once real torque or repeated assembly is involved.