M16 vs M18 bolt size comparison
M16 runs a 16 mm major diameter with 2.0 mm coarse pitch, while M18 steps to 18 mm and 2.5 mm coarse pitch.
Hex grows from 24 mm to 27 mm keys, and tap drills move from 14.0 mm to 15.5 mm pilots for coarse threads.
Open each bolt size chart hub, then run screw size conversion when you must match mixed metric bins to inch racks.
Choose the smaller fastener when sheet thickness and head height are tight; upsize when joint slip or fatigue margins demand more clamp area.
Side-by-side
| Spec | M16 | M18 |
|---|---|---|
| Major diameter | 16 mm | 18 mm |
| Coarse pitch | 2.0 mm | 2.5 mm |
| Tap drill (coarse) | 14.0 mm | 15.5 mm |
Load and tooling
Larger diameters increase tensile area roughly with d² trend; wrench fit and head height also jump, so check tool clearance before you change series.
M16 links and tools
Open the bolt size chart (M16) for hex, pitch, and tap drill in one hub table.
Use tap drill size when pitch differs from coarse or you need a quick recalculation.
Run the thread identifier after you measure major diameter and pitch on a sample thread.
Compare stocked inch hardware with screw size conversion when you cross-shop bins.
Convert pitch units with the thread pitch chart tool when drawings mix mm and TPI.
Review metric vs unc thread naming before you mix UNC taps with metric holes.
Neighbor metric hub: bolt size chart (M15) for the next smaller shank.
Neighbor metric hub: bolt size chart (M17) for the next larger shank.