DIN & ISO Screw Standards

Why two numbering systems exist

DIN standards were issued by the German standards institute and became the working language of European engineering drawings. ISO later published international equivalents, and many DIN standards were formally withdrawn in favour of them. In practice both survive: drawing offices carry decades of legacy documentation in DIN, while new specifications and export paperwork increasingly use ISO.

For most head profiles the two are dimensionally very close. They are not always identical, and head diameter or height can differ enough to matter in a counterbore or a tight assembly. Where the fit is critical, name the exact standard on your drawing and we will manufacture to it rather than substituting an equivalent.

Machine screw head standards: DIN to ISO

We manufacture machine screws to these dimensional standards across the M2 to M16 range in both coarse and fine pitch.

Self tapping and wood screw standards

The ISO 1481, 1482 and 1483 series covers slotted tapping screws, thread sizes ST 2.2 to ST 9.5. The DIN 95, 96 and 97 wood screws are a separate family and have no direct equivalent in that series, so a drawing calling for one of them should be quoted against the DIN number.

Our self tapping screws are produced in Type A, Type AB and Type B thread forms per the ISO 1478 series, and our wood screws and chipboard screws follow the equivalent dimensional conventions.

Thread tolerance classes

ISO 965 defines how tightly the thread is held. The number is the tolerance grade and the letter is the position, which sets the allowance between mating parts.

External threads use lower case letters, internal threads use upper case. Unless a drawing states otherwise, we produce to 6g, which leaves room for a plated finish without binding.

Property classes for steel screws

ISO 898-1 marks strength with a two-part number. The first part is one hundredth of the nominal tensile strength in megapascals. The second is ten times the ratio of yield strength to tensile strength. Multiply them to get the approximate yield.

Stainless steel fasteners use a different system under ISO 3506, written as A2-70 or A4-80, where the letter and number give the grade and the strength.

How to write a complete specification

A fully defined part removes ambiguity and prevents re-quoting. Include:

• Standard: for example DIN 7985 or ISO 7045.
• Thread and length: M6 x 25, with pitch stated if fine.
• Property class or material: 8.8 steel, or A2 stainless.
• Thread tolerance: 6g unless otherwise required.
• Drive: Philips, Pozidriv or Torx, with size if known. See the drive types guide.
• Finish: zinc, nickel, black oxide or a zinc-flake coating. See the finishes guide.

Example: ISO 7045 M6 x 25, class 8.8, 6g, PZ2, zinc plated. That is unambiguous in any drawing office in the world.

Manufacturing to your standard

C S Fasteners manufactures to DIN and ISO dimensional standards so parts drop into your existing bill of materials without re-qualification. For anything outside the published standards, our custom line produces made-to-drawing and made-to-sample parts, including non-standard heads, drives, thread forms and finishes.

See also the screw size chart and the guide to importing screws from India.