M16 clearance hole size

How to pick close, normal or loose

All three holes let a M16 bolt pass; the difference is how much room is left around the shank. Normal fit (17.5 mm) is the default for almost all general assembly — enough slack to line parts up without hand-fitting. Choose close fit (17 mm) when location matters and you want the bolt to hold parts in register; choose loose fit (18.5 mm) when you need to absorb hole-to-hole misalignment across a bolt pattern or thermal movement.

Why the hole is bigger than the bolt

A bolt clamps by tension, not by its shank touching the hole wall, so the through-hole is always drilled oversize. The extra room accommodates thread run-out, paint, plating and the real-world scatter of drilled-hole position. Making the hole a tight sliding fit on the bolt is a common mistake — it fights assembly and does nothing for joint strength, which comes from preload. If you need a bolt to precisely locate parts, use a reamed hole with a shoulder bolt or dowel, not a tight clearance hole.

Threads that use this hole

Clearance depends only on the nominal M16 diameter, not the thread pitch, so every M16 thread shares it: M16, M16x1.5. For the tapped side and tightening spec, see those pages.