M27 x 2.0 tap drill size
Drill 25.0 mm for an M27 x 2.0 fine thread: the 27 mm major diameter minus the 2.0 mm pitch, giving about 77% thread.
| Drill | mm | inch | Thread % | Typical use |
|---|---|---|---|---|
| 25.0 mm (ISO 2306) | 25.0 | 0.9843 | 77.0% | General purpose |
| 63/64" (inch drill) | 25.0 | 0.9844 | 76.9% | General purpose |
| 25.5 mm | 25.5 | 1.0039 | 57.7% | Low engagement: check strength |
| Thread | Tap drill | Tap drill (in) | Clearance (ISO 273 medium) |
|---|---|---|---|
| M22 x 1.5 | 20.5 mm | 0.8071 in | 24.0 mm |
| M24 x 2.0 | 22.0 mm | 0.8661 in | 26.0 mm |
| M27 x 2.0 (this page) | 25.0 mm | 0.9843 in | 30.0 mm |
| M30 x 2.0 | 28.0 mm | 1.1024 in | 33.0 mm |
| M36 x 3.0 | 33.0 mm | 1.2992 in | 39.0 mm |
Practical notes
Drilling 25.0 mm in one pass puts a lot of load on the spindle and workholding. Pilot-drill first, then open up to size; an undersize hole is the most common cause of a seized or broken tap at this size.
Tapping torque rises steeply with diameter. On a machine use a tapping head or rigid tapping; for one-off or high-value parts, thread milling avoids the risk of a broken tap and lets you adjust the fit. Threads in tubes or bosses this size are often single-point cut on a lathe instead.
Typical engagement lengths: about 1 × diameter in steel, 1.5 × in cast iron or brass and 2 × in aluminium. In softer materials a longer engagement does more for strength than a tighter tap drill.
Large fine-pitch threads such as M27 x 2.0 are typical on shafts, bearing locknuts and thin-walled housings, where a coarse thread would cut too deep into the wall. The shallower thread makes drill size more critical: a 0.1 mm change shifts engagement by about 4 percentage points.
Clearance holes come from ISO 273: fine (close) 28.0 mm, medium (normal) 30.0 mm, coarse (loose) 32.0 mm. Use fine for location, medium as the default and coarse when hole positions vary.
FAQ
What size drill for an M27 x 2.0 tap?
Use a 25.0 mm drill (0.9843 in) for a cut M27 x 2.0 tap, per ISO 2306 (major diameter minus pitch). It gives about 77% thread.
What clearance hole for an M27 bolt?
ISO 273 gives 28.0 mm (fine/close), 30.0 mm (medium/normal) and 32.0 mm (coarse/loose) for M27, whatever the pitch. Medium is the usual default.
What inch drill can I use for an M27 x 2.0 tap?
The closest inch drill is 63/64" (0.9844 in, 25.0 mm), which gives about 77% thread on M27 x 2.0.
How is M27 x 2.0 different from other M27 pitches?
Same 27 mm major diameter, different pitch, so a different tap drill: M27 x 3.0 (24.0 mm drill). The taps and bolts are not interchangeable with M27 x 2.0 (25.0 mm drill).
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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