Engineering catalogues, including this one, group standards into pairs: DIN 912 with ISO 4762, DIN 934 with ISO 4032, DIN 125 A with ISO 7089. The word "equivalent" is doing a lot of work in that sentence, and it is worth knowing exactly how much.

Three levels of equivalence

It helps to separate the claim into three questions.

Do the dimensions match? For most DIN/ISO pairs the dimension tables are identical column for column. DIN 912 and ISO 4762 both give dk, k, s and b with the same values across the size range, so a screw meeting either standard fits the same hole.

Do the mechanical properties match? Here they often diverge. The clearest case on this site is washers: DIN 125 A is specified at 140 HV while ISO 7089 is 200 HV. Identical dimensions, different hardness. A 140 HV washer under a class 10.9 bolt can deform before the bolt reaches preload, and the washer looks identical while behaving differently.

Do the marking and testing requirements match? These rarely affect fit but they matter for traceability. ISO standards generally require more explicit head marking (class and manufacturer) than the equivalent DIN, which is why an ISO part usually carries more stampings.

Where substitutions go wrong

The dangerous case is a difference that is real but small. Two examples on this site:

  • DIN 7991 and ISO 10642 both use a 90 degree countersink, so the same hole accepts both. But the ISO version's maximum head diameter is slightly smaller, so in a hole cut to the upper end of the DIN tolerance the ISO screw bears on less area. The joint assembles, looks correct, and has less margin.
  • DIN 934 and ISO 4032 are interchangeable in practice, but ISO 4032 specifies chamfers on both ends. A cheap DIN 934 with a single chamfer assembles fine and fails an incoming inspection.

Neither of these will show up in a visual check. Both show up in a dimensional inspection.

How to verify a substitution

  1. Compare the governing dimension, not the whole table. For a screw that is usually the head diameter and the thread; for a washer it is the inside diameter, outside diameter and thickness.
  2. Compare the property requirement — hardness for washers, class for bolts and nuts. The comparison pages do exactly this field by field and state where the two differ.
  3. For safety-critical joints, ask for a dimensional report rather than accepting the equivalence claim. The cost of the report is far below the cost of a rejected assembly.

The comparison section covers each pair in the database with the rows that actually differ, rather than a blanket statement that they are the same.