BenchReference

M3 × 0.5 Thread

Recommended tap drill 2.5 mm
Tap drill Ø 0.0984″ / 2.5 mm
Major Ø 0.1181″ / 3 mm
Pitch 0.5 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

DesignationM3 × 0.5
Thread familyISO metric coarse
Nominal sizeM3
Basic major diameter 0.1181″ / 3 mm
Pitch0.5 mm
Recommended tap drill 2.5 mm (0.0984″ / 2.5 mm)
P = 0.5 mm 60° major Ø 3 mm 60° thread form (UN / ISO) — schematic

Tap drill options by thread engagement

Any of these standard drills produces a usable engagement for M3 × 0.5; smaller drills give stronger threads but higher tapping torque. Percentages use the conventional approximation (60° thread form).

#40 78.6% 2.5 mm ★ 77% 2.6 mm 61.6% 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
#40 0.0980 2.489 78.6%
2.5 mm — chart recommendation 0.0984 2.5 77%
#39 0.0995 2.527 72.8%
#38 0.1015 2.578 65%
2.6 mm 0.1024 2.6 61.6%

Nearest drills to the tap drill in other systems

Drill Size vs 2.5 mm Resulting engagement
#40 0.0980″ / 2.489 mm −0.011 mm 78.6%

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 2.5 mm tap drill threads cut into the material 3.4 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 3.2 mm 0.1260 3.2
normal 3.4 mm 0.1339 3.4
loose 3.6 mm 0.1417 3.6

Hex bolt & nut dimensions

For a standard hex bolt (ISO 4014/4017) and style-1 nut (ISO 4032) in this size.

Wrench / socket size (bolt head) 5.5 mm
Head height 2 mm
Nut thickness 2.4 mm
Compatible nut M3 × 0.5 hex nut
Head — top view Bolt — side view Nut — side view width across flats = 5.5 mm wrench head height 2 mm thickness 2.4 mm

Basic (nominal) dimensions. See the wrench & socket size charts for all sizes and the metric ↔ SAE socket comparison.

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). ISO 4014 / ISO 4017, Hexagon head bolts and screws (ISO). ISO 4032, Hexagon regular nuts, style 1 (ISO). Engagement percentages use the conventional approximation (engagement = (major − drill) ÷ (1.29904 × pitch)) and are guidance, not a tolerance specification. See all data sources.