Washer Size Chart (ISO 7089 Flat Washers)
Dimensions of ISO 7089 normal-series plain washers from M3 to M24. Hardness class is 200 HV, above the 140 HV of the older DIN 125 washers.
| Nominal size | Inside dia. d1 (mm) | Outside dia. d2 (mm) | Thickness h (mm) |
|---|
Standard: ISO 7089 · Data checked: 2026-10-14
Frequently asked questions
What is the difference between ISO 7089 and DIN 125?
The dimensions are interchangeable but the hardness class is not: ISO 7089 is 200 HV and DIN 125 is 140 HV. Since the two look identical, a drawing that specifies both dimensions and hardness can be supplied with the wrong one and nobody notices until the joint fails to hold preload.
When do I need a hardened washer?
Whenever the bolt class is high enough that a soft washer would crush before the bolt reaches preload — class 10.9 and 12.9 are the usual cases. Also on soft base material, where the washer spreads the load rather than just protecting the surface.
What is the difference between a flat and a spring washer?
A flat washer spreads load and protects the surface. A spring (split) washer adds a small spring force intended to resist loosening — but its effect is modest compared with proper preload or a thread-locking compound, and it is not a substitute for either.
Why is the hole in the washer bigger than the bolt?
To clear the thread. The washer has to pass over the threaded portion, so its inside diameter is slightly larger than the bolt's nominal diameter — for M10, the washer hole is 10.5 mm. That clearance is deliberate, not sloppy manufacturing.