# 977 — Fastener standard equivalences: DIN to ISO / EN crossover

For 977, fastener description is Weld bosses/OD differ by series; iso equivalent is 21670; interchangeability is Check spec, recorded from its source on 2026-08-12.

- **DIN standard:** 977 _(verified: appears in the quote below)_
- **Fastener description:** Weld bosses/OD differ by series.
- **ISO equivalent:** 21670 _(verified: appears in the quote below)_
- **Interchangeability:** Check spec _(verified: appears in the quote below)_

## What the source says

> DIN 977 | ISO 21670 | Check spec

## Sources disagree

More than one authority states this, and they do not state the same
thing. Both are reproduced with the source each came from.

### Fastener description

monsterbolts.com says fastener description is **Weld bosses/OD differ by series.**, as of 2026-08-12.

> DIN 977 | ISO 21670 | Check spec

Source: https://monsterbolts.com/pages/common-din-numbers-for-metric-fasteners

trfastenings.com says fastener description is **Hexagon Weld Nuts with flange**, as of 2026-08-12.

> DIN 977 | ISO 21670 | | Hexagon Weld Nuts with flange |

Source: https://www.trfastenings.com/knowledge-base/engineering-data/fastener-standards


## Source

- https://monsterbolts.com/pages/common-din-numbers-for-metric-fasteners
- https://www.trfastenings.com/knowledge-base/engineering-data/fastener-standards

Last verified: 2026-08-12. Review by: 2028-08-11.
Part of [Fastener standard equivalences: DIN to ISO / EN crossover](https://referencesource.org/fastener-thread-standard-equivalence/).