M1.6 tap drill size
An M1.6 (0.35 mm pitch) tap needs a 1.25 mm drill, about 77% thread. At this size the tap is the weak link, so tap by hand, lubricate well and clear chips often.
| Drill | mm | inch | Thread % | Typical use |
|---|---|---|---|---|
| 3/64" (inch drill) | 1.19 | 0.0469 | 90.0% | Tight: high tapping torque, tap breakage risk |
| 1.2 mm | 1.2 | 0.0472 | 88.0% | Tight: high tapping torque, tap breakage risk |
| 1.25 mm (ISO 2306) | 1.25 | 0.0492 | 77.0% | General purpose |
| 1.3 mm | 1.3 | 0.0512 | 66.0% | Hard or tough material, deep or blind holes |
| Thread | Tap drill | Tap drill (in) | Clearance (ISO 273 medium) |
|---|---|---|---|
| M1.6 x 0.35 (this page) | 1.25 mm | 0.0492 in | 1.8 mm |
| M2 x 0.4 | 1.6 mm | 0.0630 in | 2.4 mm |
| M2.5 x 0.45 | 2.05 mm | 0.0807 in | 2.9 mm |
| M3 x 0.5 | 2.5 mm | 0.0984 in | 3.4 mm |
| M3.5 x 0.6 | 2.9 mm | 0.1142 in | 3.9 mm |
Practical notes
Taps this small (0.35 mm pitch) snap easily and are hard to extract. Use a tap wrench or a sensitive tapping stand, turn back every half to one turn to break chips, and keep thread depth to about 1.5 × diameter; deeper threads add almost no strength.
In aluminium, brass and free-machining steel a thread-forming tap is often more reliable at this size because there are no chips to jam. It needs the larger form-tap drill (about 1.43 mm, D − 0.5 × P; check the tap maker's chart), not the 1.25 mm cut-tap drill.
For plastic or 3D-printed parts that are assembled repeatedly, a threaded insert usually outlasts an M1.6 thread tapped into the base material.
Clearance holes come from ISO 273: fine (close) 1.7 mm, medium (normal) 1.8 mm, coarse (loose) 2.0 mm. Use fine for location, medium as the default and coarse when hole positions vary.
FAQ
What size drill for an M1.6 tap?
Use a 1.25 mm drill (0.0492 in) for a cut M1.6 x 0.35 tap, per ISO 2306 (major diameter minus pitch). It gives about 77% thread.
What clearance hole for an M1.6 bolt?
ISO 273 gives 1.7 mm (fine/close), 1.8 mm (medium/normal) and 2.0 mm (coarse/loose) for M1.6, whatever the pitch. Medium is the usual default.
What inch drill can I use for an M1.6 tap?
The closest inch drill is 3/64" (0.0469 in, 1.19 mm), which gives about 90% thread on M1.6 x 0.35. That is noticeably different from the metric drill, so use it only if the metric size is unavailable.
Sources: ISO 261 — ISO general purpose metric screw threads, general plan (pitches) · ISO 724 — basic dimensions (minor diameter D1 = D − 1.0825 P) · ISO 2306 — drills for use prior to tapping (tap drill = D − P) · ISO 273 — clearance holes for bolts and screws · Machinery's Handbook — percentage-of-thread formula
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