Need a rubber washer in millimeters? Our catalog is sized in inches, but because rubber compresses and conforms, the nearest fractional-inch washer is almost always a working match for a metric spec. Use the conversion tables below to jump from your mm dimension straight to the in-stock size.
Metric OD → nearest inch washer
| Metric OD | Exact inches | Nearest stocked OD |
|---|---|---|
| 8 mm | 0.315" | 5/16" (0.3125") |
| 10 mm | 0.394" | 3/8" (0.375") |
| 12 mm | 0.472" | 1/2" (0.5") |
| 16 mm | 0.630" | 5/8" (0.625") |
| 20 mm | 0.787" | 3/4" or 13/16" |
| 25 mm | 0.984" | 1" (1.0") |
| 32 mm | 1.260" | 1-1/4" (1.25") |
| 40 mm | 1.575" | 1-9/16" or 1-5/8" |
| 50 mm | 1.969" | 2" (2.0") |
| 75 mm | 2.953" | 3" (3.0") |
| 100 mm | 3.937" | 4" (4.0") |
Metric ID → nearest inch (matches metric bolts)
| Bolt | Exact inches | Nearest stocked ID |
|---|---|---|
| M3 | 0.118" | 1/8" (0.125") |
| M5 | 0.197" | 3/16" (0.1875") |
| M6 | 0.236" | 1/4" (0.25") |
| M8 | 0.315" | 5/16" (0.3125") |
| M10 | 0.394" | 3/8" (0.375") |
| M12 | 0.472" | 1/2" (0.5") |
| M16 | 0.630" | 5/8" (0.625") |
| M20 | 0.787" | 13/16" (0.8125") |
Metric thickness → nearest inch
2 mm ≈ 1/16" (0.0625") · 2.5 mm ≈ 3/32" (0.09375") · 3 mm ≈ 1/8" (0.125") · 5 mm ≈ 3/16" (0.1875") · 6 mm ≈ 1/4" (0.25") · 10 mm ≈ 3/8" (0.375") · 12 mm ≈ 1/2" (0.5").
Sizing rules for metric substitution
ID: the nearest inch ID should be equal to or a hair larger than your bolt so it slides on — for a bolt clearance fit, going up one stocked ID is always safe. OD: ±1 mm rarely matters as long as the washer covers the hole or seat with margin. Thickness: rubber compresses ~20–30% under proper torque, so a 3 mm spec and a 1/8" (3.18 mm) washer behave identically. All sizes come in all seven materials — pick chemistry with the material comparison and confirm dimensions with the measuring guide and size chart.
Need an exact metric dimension for a production run? Contact us for custom-cut quotes.
FAQ
Can I use an inch rubber washer for a metric bolt?
Yes in nearly all cases — match the ID to the bolt (equal or slightly larger) and rubber's conformability handles the fractional difference. M8 on a 5/16" ID washer differs by 0.06 mm.
What is an 8mm OD rubber washer in inches?
8 mm is 0.315" — a 5/16" OD (0.3125") rubber washer is the direct substitute.
Do you stock true metric-molded washers?
Our stock line is fractional-inch in 1,700+ size combinations. For exact metric molds or cuts in volume, request a custom quote.