Washers reference
Washer size guide: measure the hole, then identify the series
Why a washer hole is larger than its named fastener and why inch narrow and wide washers can produce two correct openings.
Reviewed against GaugeFox data and the sources below · Updated August 4, 2026
Common ISO 7089 metric hole ranges
The opening must clear the fastener, so an M6 washer does not have a 6.00 mm hole. GaugeFox uses the published normal-series hole range instead of treating one midpoint as exact.
| Likely fastener fit | Standard hole range |
|---|---|
| M3 | 3.20–3.38 mm |
| M4 | 4.30–4.48 mm |
| M5 | 5.30–5.48 mm |
| M6 | 6.40–6.62 mm |
| M8 | 8.40–8.62 mm |
| M10 | 10.50–10.77 mm |
| M12 | 13.00–13.27 mm |
| M14 | 15.00–15.27 mm |
| M16 | 17.00–17.27 mm |
Inch Type A narrow and wide openings
For several inch sizes, the Type A narrow and wide series have different basic openings. They are often sold using SAE-style and USS-style language, but retail naming is not consistent enough to replace the measurement.
| Likely fastener fit | Narrow opening | Wide opening |
|---|---|---|
| 1/4 in | 0.276–0.296 in | 0.307–0.327 in |
| 5/16 in | 0.339–0.359 in | 0.370–0.390 in |
| 3/8 in | 0.401–0.421 in | 0.433–0.453 in |
| 7/16 in | 0.464–0.484 in | 0.495–0.515 in |
| 1/2 in | 0.526–0.546 in | 0.557–0.577 in |
| 5/8 in | 0.649–0.686 in | 0.681–0.718 in |
| 3/4 in | 0.805–0.842 in | Shared opening |
The hole does not fully identify the washer
- Outside diameter separates narrow, wide, fender, and specialty patterns.
- Thickness affects load distribution and stack height.
- Material and finish cannot be confirmed from dimensions alone.
- A worn, punched, or distorted hole may no longer match its original range.
Reference trail
Sources and review method
These source pages identify the standards or industry references used for this guide. Full standards may require purchase. The guide is an identification aid, not a substitute for a calibrated inspection or the complete applicable standard.
Read the editorial standardUse it at the bench
Put these references on your Android screen.
GaugeFox adds calibrated on-screen gauges, searchable nearby sizes, and a local Parts Bin to the reference data in this guide.