Quick answer: use a rubber washer whose ID equals the bolt size (a 1/4" bolt takes a 1/4" ID washer), an OD about 2–3 times the bolt, and 1/16"–1/8" thickness for sealing. Metric bolt? Jump to M3 · M4 · M5 · M6 · M8 · M10 · M12 · M16 · M20.
Steel washers are named after the bolt they fit, but rubber washers are sold by their real dimensions: outside diameter (OD) x inside diameter (ID) x thickness. This chart turns a bolt or screw size into the exact rubber washer size, and lists the sizes we have in stock to ship today for each one.
Bolt size to rubber washer chart
| Bolt / screw | Shank diameter | Rubber washer ID | Sealing OD range | In stock now |
|---|---|---|---|---|
| #4 screw | 0.112" (2.8 mm) | 1/8" | 0.22"–0.34" | 10 |
| #6 screw | 0.138" (3.5 mm) | 1/8" (stretches over a #6; use 3/16 for a loose fit) | 0.28"–0.41" | 10 |
| #8 screw | 0.164" (4.2 mm) | 3/16" | 0.33"–0.49" | 8 |
| #10 screw / bolt | 0.190" (4.8 mm) | 3/16" (snug; rubber stretches the last few thousandths) | 0.38"–0.57" | 8 |
| 1/4" bolt | 0.250" (6.3 mm) | 1/4" | 0.50"–0.75" | 10 |
| 5/16" bolt | 0.3125" (7.9 mm) | 5/16" | 0.62"–0.94" | 6 |
| 3/8" bolt | 0.375" (9.5 mm) | 3/8" | 0.75"–1.12" | 12 |
| 7/16" bolt | 0.4375" (11.1 mm) | 7/16" | 0.88"–1.31" | 4 |
| 1/2" bolt | 0.500" (12.7 mm) | 1/2" | 1.00"–1.50" | 8 |
| 9/16" bolt | 0.5625" (14.3 mm) | 9/16" | 1.12"–1.69" | 2 |
| 5/8" bolt | 0.625" (15.9 mm) | 5/8" | 1.25"–1.88" | 2 |
| 3/4" bolt | 0.750" (19.0 mm) | 3/4" | 1.50"–2.25" | 4 |
| 7/8" bolt | 0.875" (22.2 mm) | 7/8" | 1.75"–2.62" | 1 |
| 1" bolt | 1.000" (25.4 mm) | 1" | 2.00"–3.00" | 5 |
Three rules for choosing the size
- ID: same as the bolt. Rubber stretches, so a washer with the bolt's nominal ID slides on with a little push and seals around the shank. A bigger hole leaves a leak path.
- OD: 2–3x the bolt for sealing, or match the steel washer. A wider washer spreads the clamping force over soft or thin material (sheet metal, plastic, roofing). When the rubber goes under a steel washer, make the OD the same so the steel presses the whole rubber face evenly.
- Thickness: 1/16" to seal, 1/8" for general use, 3/16"–1/4" to cushion. Thin washers seal flat, smooth faces; thicker ones fill uneven surfaces and absorb vibration. See the thickness guide.
Stacking with a steel washer (USS and SAE sizes)
Standard plain steel washers (ANSI B18.22.1) for common bolts. USS washers are the wide ones from the hardware bin; SAE washers are narrower.
| Bolt | USS steel ID / OD | SAE steel ID / OD | Rubber washer to match USS |
|---|---|---|---|
| 1/4" | 5/16" / 3/4" | 0.281" / 0.625" | 3/4" OD |
| 5/16" | 3/8" / 7/8" | 0.344" / 0.688" | 7/8" OD |
| 3/8" | 7/16" / 1" | 0.406" / 0.812" | 1" OD |
| 1/2" | 9/16" / 1-3/8" | 0.531" / 1.062" | 1-3/8" OD |
| 5/8" | 11/16" / 1-3/4" | 0.656" / 1.312" | 1-3/4" OD |
| 3/4" | 13/16" / 2" | 0.812" / 1.469" | 2" OD |
In-stock rubber washers by bolt size
Each link goes to the product page; the material in brackets is the one in stock. Every size is also listed in all seven materials and can be ordered.
Rubber washers for a #4 screw
- 1/4" OD x 1/8" ID x 1/32" thick (Neoprene)
- 1/4" OD x 1/8" ID x 1/16" thick (Neoprene)
- 1/4" OD x 1/8" ID x 3/32" thick (EPDM)
- 5/16" OD x 1/8" ID x 1/32" thick (Neoprene)
- 5/16" OD x 1/8" ID x 1/16" thick (Neoprene)
- 5/16" OD x 1/8" ID x 3/32" thick (EPDM)
- 3/8" OD x 1/8" ID x 1/16" thick (Neoprene)
- 3/8" OD x 1/8" ID x 3/32" thick (EPDM)
- 7/16" OD x 1/8" ID x 1/16" thick (Neoprene)
- 7/16" OD x 1/8" ID x 3/32" thick (EPDM)
Rubber washers for a #6 screw
- 1/4" OD x 1/8" ID x 1/32" thick (Neoprene)
- 1/4" OD x 1/8" ID x 1/16" thick (Neoprene)
- 1/4" OD x 1/8" ID x 3/32" thick (EPDM)
- 5/16" OD x 1/8" ID x 1/32" thick (Neoprene)
- 5/16" OD x 1/8" ID x 1/16" thick (Neoprene)
- 5/16" OD x 1/8" ID x 3/32" thick (EPDM)
- 3/8" OD x 1/8" ID x 1/16" thick (Neoprene)
- 3/8" OD x 1/8" ID x 3/32" thick (EPDM)
- 7/16" OD x 1/8" ID x 1/16" thick (Neoprene)
- 7/16" OD x 1/8" ID x 3/32" thick (EPDM)
Rubber washers for a #8 screw
- 3/8" OD x 3/16" ID x 1/16" thick (Silicone)
- 3/8" OD x 3/16" ID x 3/32" thick (EPDM)
- 7/16" OD x 3/16" ID x 3/32" thick (EPDM)
- 1/2" OD x 3/16" ID x 1/16" thick (Neoprene)
- 1/2" OD x 3/16" ID x 3/32" thick (EPDM)
- 9/16" OD x 3/16" ID x 3/32" thick (EPDM)
- 5/8" OD x 3/16" ID x 3/32" thick (Neoprene)
- 1-1/8" OD x 3/16" ID x 1/8" thick (Neoprene)
Rubber washers for a #10 screw / bolt
- 3/8" OD x 3/16" ID x 1/16" thick (Silicone)
- 3/8" OD x 3/16" ID x 3/32" thick (EPDM)
- 7/16" OD x 3/16" ID x 3/32" thick (EPDM)
- 1/2" OD x 3/16" ID x 1/16" thick (Neoprene)
- 1/2" OD x 3/16" ID x 3/32" thick (EPDM)
- 9/16" OD x 3/16" ID x 3/32" thick (EPDM)
- 5/8" OD x 3/16" ID x 3/32" thick (Neoprene)
- 1-1/8" OD x 3/16" ID x 1/8" thick (Neoprene)
Rubber washers for a 1/4" bolt
- 1/2" OD x 1/4" ID x 3/32" thick (EPDM)
- 5/8" OD x 1/4" ID x 1/16" thick (Neoprene)
- 5/8" OD x 1/4" ID x 3/32" thick (EPDM)
- 3/4" OD x 1/4" ID x 1/16" thick (Silicone)
- 3/4" OD x 1/4" ID x 3/32" thick (Neoprene)
- 3/4" OD x 1/4" ID x 1/8" thick (Neoprene)
- 3/4" OD x 1/4" ID x 3/16" thick (Silicone)
- 7/8" OD x 1/4" ID x 1/32" thick (Neoprene)
- 1-1/2" OD x 1/4" ID x 1/16" thick (Neoprene)
- 2" OD x 1/4" ID x 1/8" thick (Neoprene)
Rubber washers for a 5/16" bolt
- 1/2" OD x 5/16" ID x 1/32" thick (Neoprene)
- 9/16" OD x 5/16" ID x 3/32" thick (EPDM)
- 5/8" OD x 5/16" ID x 1/16" thick (Neoprene)
- 11/16" OD x 5/16" ID x 3/32" thick (Neoprene, EPDM)
- 3/4" OD x 5/16" ID x 1/16" thick (Neoprene)
- 7/8" OD x 5/16" ID x 1/16" thick (Neoprene)
Rubber washers for a 3/8" bolt
- 5/8" OD x 3/8" ID x 3/32" thick (EPDM)
- 3/4" OD x 3/8" ID x 1/16" thick (Neoprene, Silicone)
- 13/16" OD x 3/8" ID x 3/32" thick (EPDM)
- 13/16" OD x 3/8" ID x 1/8" thick (Neoprene)
- 7/8" OD x 3/8" ID x 1/16" thick (Neoprene)
- 1" OD x 3/8" ID x 1/32" thick (Neoprene)
- 1" OD x 3/8" ID x 1/16" thick (Neoprene)
- 1" OD x 3/8" ID x 1/8" thick (Neoprene)
- 1-1/8" OD x 3/8" ID x 1/8" thick (Neoprene)
- 1-1/4" OD x 3/8" ID x 1/16" thick (Neoprene)
- 1-3/8" OD x 3/8" ID x 3/16" thick (Neoprene)
- 1-1/2" OD x 3/8" ID x 1/16" thick (Neoprene)
Rubber washers for a 7/16" bolt
- 11/16" OD x 7/16" ID x 3/8" thick (Neoprene)
- 3/4" OD x 7/16" ID x 1/8" thick (Neoprene)
- 13/16" OD x 7/16" ID x 1/4" thick (Neoprene)
- 15/16" OD x 7/16" ID x 1/16" thick (Neoprene)
Rubber washers for a 1/2" bolt
- 3/4" OD x 1/2" ID x 1/16" thick (Neoprene, Viton)
- 3/4" OD x 1/2" ID x 1/4" thick (Neoprene)
- 1" OD x 1/2" ID x 1/8" thick (Neoprene)
- 1-1/16" OD x 1/2" ID x 3/32" thick (EPDM)
- 1-1/16" OD x 1/2" ID x 1/8" thick (Neoprene)
- 1-1/4" OD x 1/2" ID x 1/8" thick (Neoprene)
- 1-1/2" OD x 1/2" ID x 1/8" thick (Neoprene)
- 2" OD x 1/2" ID x 1/8" thick (Neoprene)
Rubber washers for a 9/16" bolt
- 15/16" OD x 9/16" ID x 3/8" thick (Neoprene)
- 1-1/8" OD x 9/16" ID x 1/16" thick (Neoprene)
Rubber washers for a 5/8" bolt
- 1-5/16" OD x 5/8" ID x 3/32" thick (EPDM)
- 1-5/16" OD x 5/8" ID x 1/8" thick (Neoprene)
Rubber washers for a 3/4" bolt
- 1" OD x 3/4" ID x 1/8" thick (Neoprene)
- 1-3/8" OD x 3/4" ID x 3/8" thick (Neoprene)
- 1-1/2" OD x 3/4" ID x 3/32" thick (EPDM)
- 2" OD x 3/4" ID x 1/8" thick (Neoprene)
Rubber washers for a 7/8" bolt
- 1-1/8" OD x 7/8" ID x 1/8" thick (Neoprene)
Rubber washers for a 1" bolt
- 1-3/8" OD x 1" ID x 3/32" thick (Neoprene)
- 1-1/2" OD x 1" ID x 1/4" thick (Neoprene)
- 2" OD x 1" ID x 3/32" thick (EPDM)
- 2" OD x 1" ID x 1/8" thick (Neoprene)
- 2-1/2" OD x 1" ID x 1/8" thick (Neoprene)
Not sure what bolt you have?
Measure the threaded shank with calipers, or pass it through a drill gauge: the smallest hole it fits is its size. Then see how to measure a rubber washer or the full rubber washer size chart.
FAQ
What size rubber washer fits a 1/4 inch bolt?
A 1/4" ID washer. Rubber should be snug on the shank so it seals around the bolt; pick an OD of roughly 1/2"–3/4" for sealing, or 3/4" to match a standard USS steel washer you are stacking it with.
What size washer for a 3/8 inch bolt?
A 3/8" ID rubber washer. Outside diameters of 3/4"–1-1/8" are typical; a USS steel washer for 3/8" is 1" OD, so a 1" OD rubber washer sits exactly under it.
What size washer for a 1/2 inch bolt?
A 1/2" ID rubber washer with an OD of 1"–1-1/2". The matching USS steel washer is 1-3/8" OD; SAE is about 1-1/16".
Should the rubber washer ID be bigger than the bolt?
For sealing, no: use the same nominal size so the rubber grips the shank. Go one size up (1/16") only when the washer is a spacer or cushion and has to slide on easily.
Is a "1/4 inch washer" 1/4 inch across?
No. Hardware washers are named for the bolt they fit. A 1/4" steel washer has a hole of about 5/16" and is 5/8"–3/4" across. Our rubber washers are listed by their actual OD x ID x thickness, so read all three numbers.