Tap Drill Size Chart

M27 x 1.5 Tap Drill Size

Tap drill

25.5 mm 1.0039 in

Use a 25.5 mm drill (1.0039 in) for 77.0% thread.

The drill size for a M27 x 1.5 tap is 25.5 mm (1.0039 in). If you are wondering what size drill bit a M27 x 1.5 tap needs, that is the one: it leaves 77.0% of thread, which is the figure standard tap and drill charts are built around. Below are the other holes you might want for this size - a larger drill for tough material, the form-tap hole, and the clearance holes for the bolt that goes in.

Every drill for M27 x 1.5

Tap drills and clearance drills for M27 x 1.5 (Metric fine, 1.5 mm pitch). Percent of thread is the figure stored for each drill, which reproduces from the major diameter and pitch of M27 x 1.5.
Use Drill Decimal in mm % thread
Standard tap drill Cut tap, general use (D - P) 25.5 mm 1.0039 25.50 77.0%
Inch substitute Closest inch drill if you have no metric set 1″ 1.000 25.40 82.1%
Hard material Stainless, tool steel, anything that fights the tap 26 mm 1.0236 26.00 51.3%
Form (roll) tap Theoretical 26.34 mm - starting point, check your tap maker's chart 26.5 mm 1.0433 26.50 —

Clearance holes for a M27 x 1.5 bolt

A clearance hole is not tapped. It is the hole in the part the bolt passes through, so it is always larger than the thread.

Clearance holes for M27 x 1.5 per ISO 273. Clearance depends on the bolt diameter alone, so every M27 thread shares these figures.
Fit Hole mm Hole in
Fine 28.00 1.1024
Medium 30.00 1.1811
Coarse 32.00 1.2598

M27 x 1.5 dimensions

Nominal dimensions for M27 x 1.5. The basic internal minor diameter is the hole a 100% thread would start from, which is why no tap drill is ever that small.
Dimension Inch mm
Major diameter 1.063 27.00
Basic internal minor diameter 0.9991 25.38
Pitch 0.0591 1.50
Thread designation M27 x 1.5

What the hole looks like

Cross-section of a M27 x 1.5 tapped hole, drawn to scale The drilled hole is 25.5 mm, 1.0039 inches or 25.50 millimetres across. The tap cuts outward from that wall to the major diameter of 1.063 inches. A 100 percent thread would reach in to the basic minor diameter of 0.9991 inches, shown as a dashed line; the difference is why this drill gives 77.0% of thread. major 27 mm drill 25.5 mm · 25.5 mm dashed = 100% thread at 25.38 mm
M27 x 1.5 in section, to scale. The accent line is the thread the tap cuts from a 25.5 mm hole; the dashed line is where the crest would sit at 100% thread. The gap between them is the 23.0% of thread this drill leaves behind.

Work out a different hole for M27 x 1.5

Pre-filled with M27 x 1.5. Change the material, the tap type, or which drills you actually own, and it picks the closest real drill and tells you the percent of thread you end up with. The tables above are the published figures and do not depend on this.

The general-purpose target

Tap type
Drills you have

Best drill you have, cut tap, 70% target

25.5 mm1.0039 in77.0% thread

Theoretical hole 25.64 mm

One size down, deeper thread1″ 1.000 in · 82.1%

One size up, easier tapping1-1/64″ 1.0156 in · 61.7%

For comparison, the published chart drill for M27 x 1.5 is 25.5 mm at 77.0% thread.

Notes on M27 x 1.5

Finest pitch at this diameter
M27 x 1.5 is the finest of the standard pitches at 27 mm. Fine threads suit thin walls and joints that see vibration, but the hole size matters more: the window between a weak thread and a broken tap is narrower than on M27 x 3.
Not the same as M27 x 3
M27 x 3 and M27 x 1.5 share a 27 mm major diameter but not a pitch, and they take different drills: 24 mm for M27 x 3, 25.5 mm for M27 x 1.5. The taps and the fasteners are not interchangeable.
What the standard drill gives you
25.5 mm leaves 77.0% of thread (D - P). That is in the normal 65-80% band most shop charts aim for.
Stainless, tool steel and other tough material
26 mm opens the hole to 51.3% engagement. Less material for the tap to cut means less torque and less heat, at the cost of some thread depth.
Using a form (roll) tap
A form tap displaces metal instead of cutting it, so it needs a larger hole: 26.5 mm, against a theoretical 26.34 mm. Treat that as a starting point and check your tap maker's chart.
Closest inch size
1-1/8-7 is the nearest inch thread by diameter (28.58 mm against 27 mm). It is a planning reference only. The two are not interchangeable: the pitches differ, and a bolt from one will not run into a hole tapped for the other.

Related sizes

Same diameter, different pitch

Next size up and down

Closest inch size

1-1/8-7 63/64″ · 0.9844 in · 25.00 mm · 75.8% 28.58 mm major against 27 mm

Not interchangeable. 1-1/8-7 is the nearest size by diameter, nothing more. The pitches differ, so a 1-1/8-7 fastener will not run into a M27 x 1.5 hole and forcing one will strip both.

Guides for tapping M27 x 1.5

Longer reads on the decisions behind the numbers above.

All guides →

M27 x 1.5 tap drill: common questions

What size drill bit do I need for a M27 x 1.5 tap?
A 25.5 mm drill, 1.0039 in. That leaves 77.0% of thread, which is the standard chart figure for M27 x 1.5.
What is the drill size for a M27 x 1.5 tap in inches?
The 25.5 mm tap drill measures 1.0039 in. If you only have inch drills, 1 in (1.000 in) is the closest, giving 82.1% thread.
What drill should I use for M27 x 1.5 in stainless steel?
Use 26 mm instead of 25.5 mm. It leaves 51.3% of thread rather than 77.0%, so there is less material for the tap to cut and less chance of snapping it.
Is M27 x 1.5 the same as M27 x 3?
No. Both are 27 mm threads, but the pitch differs, so the drills differ: 25.5 mm for M27 x 1.5 and 24 mm for M27 x 3. The taps and the fasteners are not interchangeable.
What is the clearance hole for an M27 x 1.5 bolt?
For a medium fit, 30 mm per ISO 273. A clearance hole is not tapped; the bolt passes straight through it.
A 4 × 6 in card with the drills for this size.