Key takeaways
- DIN 7504 has been replaced by ISO 15480 to 15483 in Europe, but buyers and factories still use DIN form letters every day.
- K = hex washer head, M = pan head, N = flat countersunk, O = raised countersunk, P = flat countersunk with ribs.
- Quote the standard, size, point, material, finish and washer on every order.
If you have ever compared quotations for “DIN 7504K 5.5 × 25” and “ISO 15480 ST5.5 × 25”, you were looking at the same screw. Here is the map.
Form letters
| DIN 7504 form | Head | ISO equivalent |
|---|---|---|
| K | Hex washer head | ISO 15480 |
| M | Pan head, cross recess | ISO 15481 |
| N | Countersunk, cross recess | ISO 15482 |
| O | Raised countersunk, cross recess | ISO 15483 |
| P | Countersunk with ribs (often with wings) | No direct ISO form |
What the standards fix, and what they leave open
Both define head dimensions, thread (ISO 1478 ST threads), minimum surface hardness, case depth and torsional strength. They do not define drill point length for every size, washer type, coating or packaging. That is where specifications drift between suppliers.
Write a complete order line
A complete line looks like this: ISO 15480 ST5.5 × 32, point #3, C1022 case hardened, Zn-Ni or ceramic 500 h, bonded EPDM washer 16 mm, 1,000 pcs per carton. With that line two factories should produce interchangeable screws.
Regional standards
Australia and New Zealand use AS 3566, which adds corrosion classes 1–4 and performance tests. North American buyers often quote inch sizes such as #12-14 × 1" with SAE J78 or ASTM C1513 for steel framing screws. We produce to all of these.
Frequently asked questions
Is DIN 7504 still valid?
DIN 7504 was withdrawn in favour of the ISO standards, but it remains widely used in trade and on drawings. Factories understand both.
What is an ST thread?
ST threads are tapping screw threads defined in ISO 1478, with a wider pitch than machine threads, designed to form their own mating thread.
