M2.5×0.45 thread

M2.5×0.45 is a coarse metric thread with a 2.5 mm (0.098") major diameter and 0.45 mm pitch. Tap it with a 2.05 mm drill; drill 2.7 mm to pass a bolt through.

The numbers

Designation

M2.5×0.45

Major diameter

2.5 mm / 0.098"

Minor diameter

2.013 mm

Pitch

0.45 mm pitch

Tap drill (75% thread)

2.05 mm — 2.05 mm

Clearance hole (close fit)

2.7 mm / 0.106"

Hex across flats

5 mm

How to measure what you have

1. Measure across the thread crests with calipers. A used M2.5×0.45 reads a little under 2.5 mm — the crests are truncated by the standard, then worn and plated, so anything from about 2.1 mm up is consistent with this size.
2. Measure the pitch: put a rule against the threads and count the distance over ten crests, then divide by ten. This one should give 0.45 mm.
3. A thread pitch gauge settles it in seconds and costs very little. Guessing between a coarse and a fine thread of the same diameter is the usual way a thread gets stripped.

Tightening torque

No torque figure is given for this size. Small and fine threads like this are generally not supplied to a strength grade, and in most assemblies the tapped material strips before the fastener yields — so a published bolt torque would be the wrong limit to work to. Tighten to snug plus a small turn, or use the figure the manufacturer of the part specifies.

Where this size turns up

• Raspberry Pi and single-board-computer standoffs
• Laptop base-cover and hinge screws
• Servo horn and gimbal hardware