Technical article · 4 min read
DIN 6923 vs ISO 4161: hex flange nuts compared
The same nut on two different drawings? Mostly — but check the property class, the bearing face and the size range before you swap one standard for the other.
A hex flange nut is a hex nut with an integral washer face. The flange spreads the clamp load over a larger area, so the joint needs no separate washer — fewer parts on the line and nothing to drop or forget.
Where the two standards come from
DIN 6923 is the German standard many automotive and machinery drawings still call up. It has largely been superseded by the European EN 1661 and the international ISO 4161, which now carry the same product. In practice you will see all three on drawings — sometimes on the same assembly.
What stays the same
For the common sizes M5 to M20 the key dimensions line up: across-flats (for example 13 mm at M8 and 15 mm at M10), flange diameter (17.9 mm max at M8, 21.8 mm max at M10) and nut height (equal to the nominal size). That is why a DIN 6923 nut and an ISO 4161 nut usually fit the same socket and the same counterbore.
What to check before you substitute
- Property class — the nut class must match the bolt class (for example class 8 nuts with 8.8 bolts, class 10 nuts with 10.9 bolts). Mechanical properties for nuts come from ISO 898-2.
- Bearing face — plain or serrated. Serrations resist loosening but mark the joint surface, so they are not used on painted or soft parts.
- Size range — the standards cover M5 to M20. M3, M4 and M24 flange nuts are made to drawing.
- Finish and torque — coating changes friction, so the tightening torque that worked with one finish may not hold with another.
Standards and values are summarised for general guidance — always work to your drawing and the current edition of the standard. Related REL page.
