Tap Drill Size Chart

M39 x 4 Tap Drill Size

Tap drill

35 mm 1.378 in

Use a 35 mm drill (1.378 in) for 77.0% thread.

The drill size for a M39 x 4 tap is 35 mm (1.378 in). If you are wondering what size drill bit a M39 x 4 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 M39 x 4

Tap drills and clearance drills for M39 x 4 (Metric coarse, 4 mm pitch). Percent of thread is the figure stored for each drill, which reproduces from the major diameter and pitch of M39 x 4.
Use Drill Decimal in mm % thread
Standard tap drill Cut tap, general use (D - P) 35 mm 1.378 35.00 77.0%
Inch substitute Closest inch drill if you have no metric set 1-3/8″ 1.375 34.93 78.4%
Hard material Stainless, tool steel, anything that fights the tap 36 mm 1.4173 36.00 57.7%
Form (roll) tap Theoretical 37.23 mm - starting point, check your tap maker's chart 37 mm 1.4567 37.00 —

Clearance holes for a M39 x 4 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 M39 x 4 per ISO 273. Clearance depends on the bolt diameter alone, so every M39 thread shares these figures.
Fit Hole mm Hole in
Fine 40.00 1.5748
Medium 42.00 1.6535
Coarse 45.00 1.7717

M39 x 4 dimensions

Nominal dimensions for M39 x 4. 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 1.5354 39.00
Basic internal minor diameter 1.365 34.67
Pitch 0.1575 4.00
Thread designation M39 x 4

What the hole looks like

Cross-section of a M39 x 4 tapped hole, drawn to scale The drilled hole is 35 mm, 1.378 inches or 35.00 millimetres across. The tap cuts outward from that wall to the major diameter of 1.5354 inches. A 100 percent thread would reach in to the basic minor diameter of 1.365 inches, shown as a dashed line; the difference is why this drill gives 77.0% of thread. major 39 mm drill 35 mm · 35 mm dashed = 100% thread at 34.67 mm
M39 x 4 in section, to scale. The accent line is the thread the tap cuts from a 35 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 M39 x 4

Pre-filled with M39 x 4. 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

1-25/64″1.3906 in35.32 mm70.8% thread

Theoretical hole 35.36 mm

One size down, deeper thread35 mm 1.378 in · 77.0%

One size up, easier tapping35.5 mm 1.3976 in · 67.4%

For comparison, the published chart drill for M39 x 4 is 35 mm at 77.0% thread.

Notes on M39 x 4

Only pitch in the data
M39 x 4 is the only pitch this chart lists at 39 mm, so there is no fine or coarse alternative to confuse it with.
What the standard drill gives you
35 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
36 mm opens the hole to 57.7% 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: 37 mm, against a theoretical 37.23 mm. Treat that as a starting point and check your tap maker's chart.
This size is usually bored, not drilled
At 39 mm, holes this big are normally bored or thread-milled rather than drilled and tapped. The 35 mm figure is here so the numbers are complete and so you can check a hole you already have; on a machine you would single-point or thread-mill the thread and bore the hole to size.
Closest inch size
1-1/2-6 is the nearest inch thread by diameter (38.1 mm against 39 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

Next size up and down

Closest inch size

1-1/2-6 1-11/32″ · 1.3438 in · 34.13 mm · 72.1% 38.1 mm major against 39 mm

Not interchangeable. 1-1/2-6 is the nearest size by diameter, nothing more. The pitches differ, so a 1-1/2-6 fastener will not run into a M39 x 4 hole and forcing one will strip both.

Guides for tapping M39 x 4

Longer reads on the decisions behind the numbers above.

All guides →

M39 x 4 tap drill: common questions

What size drill bit do I need for a M39 x 4 tap?
A 35 mm drill, 1.378 in. That leaves 77.0% of thread, which is the standard chart figure for M39 x 4.
What is the drill size for a M39 x 4 tap in inches?
The 35 mm tap drill measures 1.378 in. If you only have inch drills, 1-3/8 in (1.375 in) is the closest, giving 78.4% thread.
What drill should I use for M39 x 4 in stainless steel?
Use 36 mm instead of 35 mm. It leaves 57.7% of thread rather than 77.0%, so there is less material for the tap to cut and less chance of snapping it.
What is the clearance hole for an M39 x 4 bolt?
For a medium fit, 42 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.