Tap drills
M3 x 0.5 tap drill size
The tap drill for M3 x 0.5 is 2.5 mm, which is 0.0984 inches or 2.50 mm. That leaves about 92 percent thread engagement.
M3 x 0.5 tap drill, clearance and engagement
| Series | Metric coarse |
| Major diameter | 0.1181 in (3.00 mm) |
| Pitch | 0.5 mm |
| Tap drill | 2.5 mm (0.0984 in / 2.50 mm) |
| Thread engagement | 92% |
| Drill for 75% thread | 0.1021 in |
| Clearance, close fit | 3.2 mm (0.1260 in) |
| Nearest metric drill | 2.5 mm (0.0984 in) |
What M3 x 0.5 is used for
The standard small metric fastener in electronics, 3D printer frames, camera hardware, PCB standoffs and consumer product assembly.
If you do not have that drill
2.6 mm lowers engagement from about 92 percent to around 72 percent, which matters in aluminium and printed parts where a broken M3 tap is hard to extract.
How to tap a M3 x 0.5 thread
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Drill the hole
Use a 2.5 mm drill, 0.0984 inches or 2.50 mm. Drill square to the surface and clear the swarf on deep holes.
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Start the tap square
Start with a taper tap and check it is square in both axes within the first two turns. A tap started crooked will cut a crooked thread all the way down and cannot be corrected.
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Cut and break the chip
Turn forward about half a turn, then back a quarter turn to break the chip. Use cutting fluid on steel and stainless; aluminium and brass usually need none, though a wax stick helps in aluminium.
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Check the fit
Run the mating fastener in by hand. It should turn freely without side play. If it binds, the hole was undersized or the tap wandered.
Common questions
What size drill do I need for a M3 x 0.5 tap?
- The tap drill for M3 x 0.5 is 2.5 mm, which is 0.0984 inches or 2.50 mm. That leaves about 92 percent thread engagement. 2.6 mm lowers engagement from about 92 percent to around 72 percent, which matters in aluminium and printed parts where a broken M3 tap is hard to extract.
What is the clearance hole for a M3 x 0.5 bolt?
- 3.2 mm, which is 0.1260 inches. That is a close fit. A normal fit is one drill size larger and a loose fit two, and the looser classes are the sensible choice when the parts have to line up without reaming.
How is the M3 x 0.5 tap drill worked out?
- Subtract the pitch from the major diameter: 0.1181 inches (3 mm) minus 0.5 mm gives 2.50 mm, and 2.5 mm is the nearest standard drill. This is the metric convention and it lands near 92 percent engagement, not the 75 percent an inch chart targets.
Can I use a metric drill for a M3 x 0.5 tap?
- The closest standard metric drill is 2.5 mm, which is 0.0984 inches against 0.0984 for 2.5 mm. That changes engagement to about 92 percent, so check that figure is acceptable for your material before substituting.