Tap Drill Size Chart

M45 x 4.5 Tap Drill Size

Tap drill

40.5 mm 1.5945 in

Use a 40.5 mm drill (1.5945 in) for 77.0% thread.

The drill size for a M45 x 4.5 tap is 40.5 mm (1.5945 in). If you are wondering what size drill bit a M45 x 4.5 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 M45 x 4.5

Tap drills and clearance drills for M45 x 4.5 (Metric coarse, 4.5 mm pitch). Percent of thread is the figure stored for each drill, which reproduces from the major diameter and pitch of M45 x 4.5.
Use Drill Decimal in mm % thread
Standard tap drill Cut tap, general use (D - P) 40.5 mm 1.5945 40.50 77.0%
Inch substitute Closest inch drill if you have no metric set 1-19/32″ 1.5938 40.48 77.3%
Hard material Stainless, tool steel, anything that fights the tap 41.5 mm 1.6339 41.50 59.9%
Form (roll) tap Theoretical 43.01 mm - starting point, check your tap maker's chart 43 mm 1.6929 43.00 —

Clearance holes for a M45 x 4.5 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 M45 x 4.5 per ISO 273. Clearance depends on the bolt diameter alone, so every M45 thread shares these figures.
Fit Hole mm Hole in
Fine 46.00 1.811
Medium 48.00 1.8898
Coarse 52.00 2.0472

M45 x 4.5 dimensions

Nominal dimensions for M45 x 4.5. 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 1.7717 45.00
Basic internal minor diameter 1.5799 40.13
Pitch 0.1772 4.50
Thread designation M45 x 4.5

What the hole looks like

Cross-section of a M45 x 4.5 tapped hole, drawn to scale The drilled hole is 40.5 mm, 1.5945 inches or 40.50 millimetres across. The tap cuts outward from that wall to the major diameter of 1.7717 inches. A 100 percent thread would reach in to the basic minor diameter of 1.5799 inches, shown as a dashed line; the difference is why this drill gives 77.0% of thread. major 45 mm drill 40.5 mm · 40.5 mm dashed = 100% thread at 40.13 mm
M45 x 4.5 in section, to scale. The accent line is the thread the tap cuts from a 40.5 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 M45 x 4.5

Pre-filled with M45 x 4.5. 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

1-39/64″1.6094 in40.88 mm70.5% thread

Theoretical hole 40.91 mm

One size down, deeper thread40.5 mm 1.5945 in · 77.0%

One size up, easier tapping41 mm 1.6142 in · 68.4%

For comparison, the published chart drill for M45 x 4.5 is 40.5 mm at 77.0% thread.

Notes on M45 x 4.5

Only pitch in the data
M45 x 4.5 is the only pitch this chart lists at 45 mm, so there is no fine or coarse alternative to confuse it with.
What the standard drill gives you
40.5 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
41.5 mm opens the hole to 59.9% 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: 43 mm, against a theoretical 43.01 mm. Treat that as a starting point and check your tap maker's chart.
This size is usually bored, not drilled
At 45 mm, holes this big are normally bored or thread-milled rather than drilled and tapped. The 40.5 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 45 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 45 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 M45 x 4.5 hole and forcing one will strip both.

Guides for tapping M45 x 4.5

Longer reads on the decisions behind the numbers above.

All guides →

M45 x 4.5 tap drill: common questions

What size drill bit do I need for a M45 x 4.5 tap?
A 40.5 mm drill, 1.5945 in. That leaves 77.0% of thread, which is the standard chart figure for M45 x 4.5.
What is the drill size for a M45 x 4.5 tap in inches?
The 40.5 mm tap drill measures 1.5945 in. If you only have inch drills, 1-19/32 in (1.5938 in) is the closest, giving 77.3% thread.
What drill should I use for M45 x 4.5 in stainless steel?
Use 41.5 mm instead of 40.5 mm. It leaves 59.9% 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 M45 x 4.5 bolt?
For a medium fit, 48 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.