The rule: a rubber washer's inside diameter matches the bolt diameter. This chart maps every common bolt and screw to the washer ID to order, with the recommended OD range for normal sealing (2–3x the ID) — go wider for fender-style load spreading on soft material.
Bolt → Washer Chart
| Bolt / screw | Washer ID | Typical OD range |
|---|---|---|
| #6 screw | 5/32" | 3/8" – 1/2" |
| #8 screw | 3/16" | 7/16" – 5/8" |
| #10 screw | 3/16" – 7/32" | 1/2" – 5/8" |
| 1/4" bolt | 1/4" | 5/8" – 3/4" |
| 5/16" bolt | 5/16" | 3/4" – 1" |
| 3/8" bolt | 3/8" | 7/8" – 1-1/8" |
| 1/2" bolt | 1/2" | 1-1/8" – 1-1/2" |
| 5/8" bolt | 5/8" | 1-3/8" – 1-3/4" |
| 3/4" bolt | 3/4" | 1-5/8" – 2" |
| 1" bolt | 1" | 2"+ |
Thickness Selection
1/16" — watertight sealing under a fastener head (plumbing, roofing, deck screws). 1/8" — cushioning, anti-rattle, and vibration damping. 1/4"–1/2" — spacer and bushing duty, filling gaps between parts.
Prefer it calculated for you? Use the interactive Washer Size Finder. Then shop rubber washers by exact OD x ID x thickness — metric bolt? Convert first with the fraction–decimal–mm converter.