Look up tap drill
M16 coarse (M16 × 2) shows up on machinery bases, lifting points and structural steel. Fine M16 × 1.5 is preferred on hydraulic ports and high-vibration joints.
Recommended tap drill
14.4mm
0.5669 in
75% thread: tap drill ≈ major − pitch (16 − engagement × 1.0825 × 2).
Tap drill ≈ 16 − 2 = 14.0 mm. Fine M16 × 1.5 uses 14.5 mm. Normal clearance is 18 mm. At this diameter, tapping torque is significant — use a spiral-flute tap or thread mill in blind holes.
Formula
Major Ø 16 mm
Pitch 2 mm
Tap drill 14.4 mm
Minor Ø 13.835 mm
M16 × 2 at a glance
Full metric and imperial charts live on the thread & tap drill calculator. Other common sizes: M8 × 1.25, M10 × 1.5, M12 × 1.75, M6 × 1.
For a typical 75% thread engagement, tap drill ≈ major diameter − pitch. For M8 × 1.25 that is 8.00 − 1.25 = 6.75 mm, rounded to the standard 6.8 mm drill. Fine pitches subtract a smaller pitch and therefore use a larger drill.
A tap drill is the hole you tap (internal thread). A clearance drill is a through-hole for a bolt to pass freely. Clearance holes are given as close, normal and loose fits per common workshop practice (aligned with ISO 273 medium series).
Yes. UNC, UNF, UNEF, BSW and BSF are included with TPI, major diameter, tap drill (inch and nearest fractional), and clearance drill recommendations.
75% is the usual workshop target for strength versus tapping torque. Softer materials or difficult holes sometimes use 60–70%; high-strength joints in steel may go higher. The calculator shows the 75% recommendation and the formula so you can adjust.
M8 is a metric thread with 8 mm major diameter. 1.25 mm is the pitch (distance between crests) — the ISO coarse pitch for M8. Fine M8 variants include 1.0 mm and 0.75 mm pitch.
Other jobs people do after this one — not the same tool twice.