BenchReference

M2.5 × 0.45 Thread

Recommended tap drill 2.05 mm
Tap drill Ø 0.0807″ / 2.05 mm
Major Ø 0.0984″ / 2.5 mm
Pitch 0.45 mm

The chart recommendation gives approximately 77% thread engagement — the conventional target for average materials. It is not the only valid choice; see the options below.

Specification

DesignationM2.5 × 0.45
Thread familyISO metric coarse
Nominal sizeM2.5
Basic major diameter 0.0984″ / 2.5 mm
Pitch0.45 mm
Recommended tap drill 2.05 mm (0.0807″ / 2.05 mm)
P = 0.45 mm 60° major Ø 2.5 mm 60° thread form (UN / ISO) — schematic

Tap drill options by thread engagement

Any of these standard drills produces a usable engagement for M2.5 × 0.45; smaller drills give stronger threads but higher tapping torque. Percentages use the conventional approximation (60° thread form).

2.05 mm ★ 77% 2.1 mm 68.4% shaded = share of the full thread height the tap forms · accent line = drilled hole wall
★ = chart recommendation. A smaller drill leaves more of the thread height for the tap to form.
Drill Decimal in mm Approx. engagement
2.05 mm — chart recommendation 0.0807 2.05 77%
#46 0.0810 2.057 75.7%
#45 0.0820 2.083 71.4%
2.1 mm 0.0827 2.1 68.4%

Nearest drills to the tap drill in other systems

Drill Size vs 2.05 mm Resulting engagement
5/64″ 0.0781″ / 1.984 mm −0.066 mm 88.2%
#46 0.0810″ / 2.057 mm +0.007 mm 75.7%

Clearance holes

For a bolt or screw of this size to pass through freely. ISO 273 series (fine/medium/coarse), shown as close, normal, and loose.

Tapped hole Clearance hole 2.05 mm tap drill threads cut into the material 2.9 mm (normal fit) the tinted gap lets the bolt pass freely
Schematic — proportions exaggerated for clarity; use the table values.
Fit Drill / Ø Decimal in mm
close 2.7 mm 0.1063 2.7
normal 2.9 mm 0.1142 2.9
loose 3.1 mm 0.1220 3.1

Related threads

Data provenance. ISO 261 / ISO 724, ISO general purpose metric screw threads (ISO). ISO 2306, Drills for use prior to tapping screw threads (ISO). ISO 273, Clearance holes for bolts and screws (ISO). Engagement percentages use the conventional approximation (engagement = (major − drill) ÷ (1.29904 × pitch)) and are guidance, not a tolerance specification. See all data sources.