SwissMetric
Well-known member
Metric nuts and hexagonal bolt heads
Details can be found on pages 396 and 397 of the 2020/2021 Stahlwille PDF catalog (corresponds to print pages 394 and 395):
https://www.stahlwille.com/en_us/downloads/d07d50a7
M means metric, followed by the nominal thread diameter in mm, for example M8 for 8 mm (MF would mean metric fine, e.g. MF8). The 2nd number is the nominal across flat dimension, in some cases there are two different values because some ISO standardizing idiots found it useful to change something which worked perfectly during many decades. Here the old across flats are still widely used also for new screws.
Thread diameters within () are non-preferential sizes, I probably used the wrong word here but I can't check the ISO standard right now.
Thread Across Flats
M1.6: 3.2 mm
M2: 4 mm
M3: 5.5 mm
M4: 7 mm
M5: 8 mm
M6: 10 mm
(M7): 11 mm
M8: 13 mm
M10: 16 mm (current ISO); 17 mm
M12: 18 mm (current ISO); 19 mm
(M14): 21 mm (current ISO); 22 mm
M16: 24 mm
(M18): 27 mm
M20: 30 mm
(M22): 32 mm; 34 mm (current ISO)
M24: 36 mm
(M27): 41 mm
M30: 46 mm
(M33): 50 mm
M36: 55 mm
(M39): 60 mm
M42: 65 mm
(M45): 70 mm
M48: 75 mm
M52: 80 mm
M56: 85 mm
M60: 90 mm
M64: 95 mm
M68: 100 mm
M72: 105 mm
Where two across flats are mentioned it's recommended to get tools for both. For example during many decades M10 required 17 mm until some ISO standardizing committee decided to reduce it without any valid reason to 16 mm. As fortunately nearly no one wants 16 mm, 17 mm is still widely used. The same applies to M12 and 19 mm.
Above M72 I'd have to check the ISO standards.
Tools are typically in 5 mm increments up to exceeding 200 mm.
The largest sockets with square drive I've seen were with 3 1/2" drive, more common are 2 1/2" and 1 1/2". Above 1" square drive I've only ever seen impact sockets and impact accessories.
See e.g. the Ozat (https://ozatusa.com) catalog for some examples of very large sockets.
For high torques, hydraulic torque wrenches (up to exceeding 100'000 Nm with special cassette design) must be used though hydraulic axial tensioning is more common and much easier to perform (for example with 2000 bar (not 700 bar) hydraulics, can be done with a hand or electric pump, the one I used was IIRC from Enerpac, process is quite straightforward if threads are clean).
Details can be found on pages 396 and 397 of the 2020/2021 Stahlwille PDF catalog (corresponds to print pages 394 and 395):
https://www.stahlwille.com/en_us/downloads/d07d50a7
M means metric, followed by the nominal thread diameter in mm, for example M8 for 8 mm (MF would mean metric fine, e.g. MF8). The 2nd number is the nominal across flat dimension, in some cases there are two different values because some ISO standardizing idiots found it useful to change something which worked perfectly during many decades. Here the old across flats are still widely used also for new screws.
Thread diameters within () are non-preferential sizes, I probably used the wrong word here but I can't check the ISO standard right now.
Thread Across Flats
M1.6: 3.2 mm
M2: 4 mm
M3: 5.5 mm
M4: 7 mm
M5: 8 mm
M6: 10 mm
(M7): 11 mm
M8: 13 mm
M10: 16 mm (current ISO); 17 mm
M12: 18 mm (current ISO); 19 mm
(M14): 21 mm (current ISO); 22 mm
M16: 24 mm
(M18): 27 mm
M20: 30 mm
(M22): 32 mm; 34 mm (current ISO)
M24: 36 mm
(M27): 41 mm
M30: 46 mm
(M33): 50 mm
M36: 55 mm
(M39): 60 mm
M42: 65 mm
(M45): 70 mm
M48: 75 mm
M52: 80 mm
M56: 85 mm
M60: 90 mm
M64: 95 mm
M68: 100 mm
M72: 105 mm
Where two across flats are mentioned it's recommended to get tools for both. For example during many decades M10 required 17 mm until some ISO standardizing committee decided to reduce it without any valid reason to 16 mm. As fortunately nearly no one wants 16 mm, 17 mm is still widely used. The same applies to M12 and 19 mm.
Above M72 I'd have to check the ISO standards.
Tools are typically in 5 mm increments up to exceeding 200 mm.
The largest sockets with square drive I've seen were with 3 1/2" drive, more common are 2 1/2" and 1 1/2". Above 1" square drive I've only ever seen impact sockets and impact accessories.
See e.g. the Ozat (https://ozatusa.com) catalog for some examples of very large sockets.
For high torques, hydraulic torque wrenches (up to exceeding 100'000 Nm with special cassette design) must be used though hydraulic axial tensioning is more common and much easier to perform (for example with 2000 bar (not 700 bar) hydraulics, can be done with a hand or electric pump, the one I used was IIRC from Enerpac, process is quite straightforward if threads are clean).