ISO 4161 M20 Flange
ISO 4161 M20 is a flange nut, on a M20 × 1.5 mm metric thread. A hex nut with a wide circular flange that spreads the clamping load and behaves like an integrated washer. Speeds up assembly versus nut + washer.
Dimensions
- Standard
- ISO 4161
- Type
- Flange nut
- Size
- M20
- Thread
- M20 × 1.5
- Socket size s
- 30 mm
- Height m
- 20 mm
- Flange diameter dc
- 42.8 mm
- Drive
- External hexagon
- Head
- Flange
Nominal values in millimetres as published in ISO 4161. Estimated weight 42.451 g per piece in steel (42.722 g in stainless), calculated from the nominal geometry — real parts vary with tolerance and head chamfers.
Thread data
Full M20 thread pageOther lengthsISO 4161 M20
All M20 specificationsInterchangeability
ISO 4161 is catalogued with DIN 6923 as its equivalent designation. Dimensions are compared field by field rather than assumed identical.
Choosing and fitting this size
ISO 4161 M20 is a M20 nut, on a 1.5 mm coarse pitch. Mating threads should be a matching class nut in the same property class.
Common stock grades are 8.8, 10.9 and 12.9 in steel, plus A2-70 and A4-80 in stainless. Class 10.9 and 12.9 carry roughly 1.25 and 1.5 times the proof load of 8.8, but they also need a properly rated mating nut — a class 8 nut under a 12.9 bolt simply moves the failure into the thread. Zinc-plated 10.9 and above should be baked to avoid hydrogen embrittlement.
For a tapped hole, M20 × 1.5 mm takes a 18.5 mm tap drill, and the external thread's minor diameter is 18.16 mm — that is the section carrying the load, not the nominal M20 figure. Thread engagement of at least one times the nominal diameter is what lets the bolt fail before the thread strips.