ASME B18.22.1 Plain Washer — Inch Series
The inch-series plain washer in the preferred series. Inside diameters are sized to the nominal bolt diameter plus clearance, matching the inch bolt range rather than metric.
Where it is used
The inch-series plain washer is used under inch bolt heads and nuts to spread the clamping load and protect the joint surface. It is specified by nominal bolt size rather than by its own diameter, so the washer is always ordered alongside the fastener it serves.
How to choose it
The table here lists the preferred series, which is the default unless a drawing calls out a narrower or wider type. Washers are graded by hardness rather than tensile strength: a washer softer than the bolt will deform before the bolt reaches its preload, silently losing clamping force. Match the hardness class to the bolt grade, and do not substitute a metric washer by inside diameter — inch washers are sized to inch bolt diameters.
Dimensions6 sizes · inches
| Bolt size | Inside diameter d1 (in) | Outside diameter d2 (in) | Thickness h (in) |
|---|---|---|---|
| 1/4 | 0.281 | 0.625 | 0.065 |
| 5/16 | 0.344 | 0.688 | 0.065 |
| 3/8 | 0.406 | 0.812 | 0.065 |
| 1/2 | 0.531 | 1.062 | 0.095 |
| 5/8 | 0.656 | 1.312 | 0.095 |
| 3/4 | 0.812 | 1.469 | 0.134 |
Nominal dimensions in inches as published in ASME B18.22.1. Tolerances, material requirements and marking are defined separately by the issuing body.
Available sizeslinked to individual specification pages
Fitting and interchange notes
Inside diameter is the bolt diameter plus clearance, so a 1/4 in washer has a 0.281 in hole, not 0.250 in. A washer that fits the bolt snugly will be undersized for the standard series and may not be the one the drawing intends. Thickness scales in steps through the range — 0.065 in up to 3/8, 0.095 in from 1/2, 0.134 in at 3/4 — so identical-looking washers from different bins can differ in thickness.