Tap Drill Size Chart

M2.5 x 0.45 Tap Drill Size

Tap drill

2.05 mm 0.0807 in

Use a 2.05 mm drill (0.0807 in) for 77.0% thread.

The drill size for a M2.5 x 0.45 tap is 2.05 mm (0.0807 in). If you are wondering what size drill bit a M2.5 x 0.45 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 M2.5 x 0.45

Tap drills and clearance drills for M2.5 x 0.45 (Metric coarse, 0.45 mm pitch). Percent of thread is the figure stored for each drill, which reproduces from the major diameter and pitch of M2.5 x 0.45.
Use Drill Decimal in mm % thread
Standard tap drill Cut tap, general use (D - P) 2.05 mm 0.0807 2.05 77.0%
Inch substitute Closest inch drill if you have no metric set #46 0.081 2.06 75.8%
Hard material Stainless, tool steel, anything that fights the tap 2.15 mm 0.0846 2.15 59.9%
Form (roll) tap Theoretical 2.3 mm - starting point, check your tap maker's chart 2.3 mm 0.0906 2.30 —

Clearance holes for a M2.5 x 0.45 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 M2.5 x 0.45 per ISO 273. Clearance depends on the bolt diameter alone, so every M2.5 thread shares these figures.
Fit Hole mm Hole in
Fine 2.70 0.1063
Medium 2.90 0.1142
Coarse 3.10 0.122

M2.5 x 0.45 dimensions

Nominal dimensions for M2.5 x 0.45. 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 0.0984 2.50
Basic internal minor diameter 0.0793 2.01
Pitch 0.0177 0.45
Thread designation M2.5 x 0.45

What the hole looks like

Cross-section of a M2.5 x 0.45 tapped hole, drawn to scale The drilled hole is 2.05 mm, 0.0807 inches or 2.05 millimetres across. The tap cuts outward from that wall to the major diameter of 0.0984 inches. A 100 percent thread would reach in to the basic minor diameter of 0.0793 inches, shown as a dashed line; the difference is why this drill gives 77.0% of thread. major 2.5 mm drill 2.05 mm · 2.05 mm dashed = 100% thread at 2.01 mm
M2.5 x 0.45 in section, to scale. The accent line is the thread the tap cuts from a 2.05 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 M2.5 x 0.45

Pre-filled with M2.5 x 0.45. 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

#450.082 in2.08 mm71.3% thread

Theoretical hole 2.09 mm

One size down, deeper thread#46 0.081 in · 75.8%

One size up, easier tapping2.1 mm 0.0827 in · 68.4%

For comparison, the published chart drill for M2.5 x 0.45 is 2.05 mm at 77.0% thread.

Notes on M2.5 x 0.45

Only pitch in the data
M2.5 x 0.45 is the only pitch this chart lists at 2.5 mm, so there is no fine or coarse alternative to confuse it with.
What the standard drill gives you
2.05 mm leaves 77.0% of thread (D - P). That is in the normal 65-80% band most shop charts aim for.
Small tap, easy to snap
At 2.5 mm this is one of the small sizes. The drill is only 0.0807 in, the tap is thinner still, and hand pressure alone can break it. Use a tap handle you can keep square, back off often, and keep the hole clear of chips.
Stainless, tool steel and other tough material
2.15 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: 2.3 mm, against a theoretical 2.3 mm. Treat that as a starting point and check your tap maker's chart.
Closest inch size
#3-48 is the nearest inch thread by diameter (2.51 mm against 2.5 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

#3-48 #47 · 0.0785 in · 1.99 mm · 75.7% 2.51 mm major against 2.5 mm

Not interchangeable. #3-48 is the nearest size by diameter, nothing more. The pitches differ, so a #3-48 fastener will not run into a M2.5 x 0.45 hole and forcing one will strip both.

Guides for tapping M2.5 x 0.45

Longer reads on the decisions behind the numbers above.

All guides →

M2.5 x 0.45 tap drill: common questions

What size drill bit do I need for a M2.5 x 0.45 tap?
A 2.05 mm drill, 0.0807 in. That leaves 77.0% of thread, which is the standard chart figure for M2.5 x 0.45.
What is the drill size for a M2.5 x 0.45 tap in inches?
The 2.05 mm tap drill measures 0.0807 in. If you only have inch drills, #46 (0.081 in) is the closest, giving 75.8% thread.
What drill should I use for M2.5 x 0.45 in stainless steel?
Use 2.15 mm instead of 2.05 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 M2.5 x 0.45 bolt?
For a medium fit, 2.9 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.