M27 is one of the standard coarse-thread sizes for hex bolts under ISO 4014 / ISO 4017. The sections below reproduce the dimensional row, list the matching tools and hole sizes, and summarize where this size is normally specified.
M27 Dimensional Row (ISO 4014 / ISO 4017)
| Size | Pitch coarse (mm) | Width across flats s (mm) | Width across corners e min (mm) | Head height k nom (mm) | Nominal diameter d (mm) | Reference standard | Notes |
|---|---|---|---|---|---|---|---|
| M27 | 3.0 | 41.0 | 45.2 | 17.0 | 27.0 | ISO 4014/4017 | Partial / fully threaded |
Spanner & Drive for M27 Hex Bolts
M27 Hex Bolts have a width across flats of 41.0 mm — fit a 41.0 mm open-ended spanner or socket. Use a 6-point socket for tight clearances and to reduce rounding; for repeated assembly choose a torque wrench so the joint preload is repeatable.
Common Applications for M27 Hex Bolts
M27 Hex Bolts are commonly specified for structural steelwork, heavy machinery foundations and large flange joints.
Installation Tips for M27 Hex Bolts
- Use a 6-point socket where access allows — 12-point sockets are more prone to rounding the corners on smaller sizes.
- On flanged or serrated variants, do NOT add a separate flat washer — the flange already spreads the load and the washer can defeat the locking serrations.
- At M27 the stretch in the bolt becomes the controlling factor — for critical joints, use angle-controlled or stretch-controlled tightening instead of pure torque.
Mating Parts for M27
For M27, pair with a M27 hex nut (ISO 4032 / DIN 934) and, where used, a M27 flat washer (ISO 7089 / DIN 125A) under the head and under the nut.
