Tap Drill Size Chart

M42 x 3 Tap Drill Size

Tap drill

39 mm 1.5354 in

Use a 39 mm drill (1.5354 in) for 77.0% thread.

Fine thread M42 x 2? Use 40 mm. (1.5748 in, 77.0% thread)

The drill size for a M42 x 3 tap is 39 mm (1.5354 in). If you are wondering what size drill bit a M42 x 3 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 M42 x 3

Tap drills and clearance drills for M42 x 3 (Metric fine, 3 mm pitch). Percent of thread is the figure stored for each drill, which reproduces from the major diameter and pitch of M42 x 3.
Use Drill Decimal in mm % thread
Standard tap drill Cut tap, general use (D - P) 39 mm 1.5354 39.00 77.0%
Inch substitute Closest inch drill if you have no metric set 1-17/32″ 1.5312 38.89 79.7%
Hard material Stainless, tool steel, anything that fights the tap 39.5 mm 1.5551 39.50 64.2%
Form (roll) tap Theoretical 40.67 mm - starting point, check your tap maker's chart 40.5 mm 1.5945 40.50 —

Clearance holes for a M42 x 3 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 M42 x 3 per ISO 273. Clearance depends on the bolt diameter alone, so every M42 thread shares these figures.
Fit Hole mm Hole in
Fine 43.00 1.6929
Medium 45.00 1.7717
Coarse 48.00 1.8898

M42 x 3 dimensions

Nominal dimensions for M42 x 3. 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 1.6535 42.00
Basic internal minor diameter 1.5257 38.75
Pitch 0.1181 3.00
Thread designation M42 x 3

What the hole looks like

Cross-section of a M42 x 3 tapped hole, drawn to scale The drilled hole is 39 mm, 1.5354 inches or 39.00 millimetres across. The tap cuts outward from that wall to the major diameter of 1.6535 inches. A 100 percent thread would reach in to the basic minor diameter of 1.5257 inches, shown as a dashed line; the difference is why this drill gives 77.0% of thread. major 42 mm drill 39 mm · 39 mm dashed = 100% thread at 38.75 mm
M42 x 3 in section, to scale. The accent line is the thread the tap cuts from a 39 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 M42 x 3

Pre-filled with M42 x 3. 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

1-35/64″1.5469 in39.29 mm69.5% thread

Theoretical hole 39.27 mm

One size down, deeper thread39 mm 1.5354 in · 77.0%

One size up, easier tapping39.5 mm 1.5551 in · 64.2%

For comparison, the published chart drill for M42 x 3 is 39 mm at 77.0% thread.

Notes on M42 x 3

Middle pitch at this diameter
At 42 mm the data holds 3 pitches: M42 x 4.5, M42 x 3, M42 x 2. M42 x 3 sits between M42 x 4.5 and M42 x 2.
Not the same as M42 x 4.5
M42 x 4.5 and M42 x 3 share a 42 mm major diameter but not a pitch, and they take different drills: 37.5 mm for M42 x 4.5, 39 mm for M42 x 3. The taps and the fasteners are not interchangeable.
What the standard drill gives you
39 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
39.5 mm opens the hole to 64.2% 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: 40.5 mm, against a theoretical 40.67 mm. Treat that as a starting point and check your tap maker's chart.
This size is usually bored, not drilled
At 42 mm, holes this big are normally bored or thread-milled rather than drilled and tapped. The 39 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 42 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

1-1/2-6 1-11/32″ · 1.3438 in · 34.13 mm · 72.1% 38.1 mm major against 42 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 M42 x 3 hole and forcing one will strip both.

Guides for tapping M42 x 3

Longer reads on the decisions behind the numbers above.

All guides →

M42 x 3 tap drill: common questions

What size drill bit do I need for a M42 x 3 tap?
A 39 mm drill, 1.5354 in. That leaves 77.0% of thread, which is the standard chart figure for M42 x 3.
What is the drill size for a M42 x 3 tap in inches?
The 39 mm tap drill measures 1.5354 in. If you only have inch drills, 1-17/32 in (1.5312 in) is the closest, giving 79.7% thread.
What drill should I use for M42 x 3 in stainless steel?
Use 39.5 mm instead of 39 mm. It leaves 64.2% of thread rather than 77.0%, so there is less material for the tap to cut and less chance of snapping it.
Is M42 x 3 the same as M42 x 2?
No. Both are 42 mm threads, but the pitch differs, so the drills differ: 39 mm for M42 x 3 and 40 mm for M42 x 2. The taps and the fasteners are not interchangeable.
What is the clearance hole for an M42 x 3 bolt?
For a medium fit, 45 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.