Sealing & Crush Washers
Washers & Retaining Rings · 9 specs
Direct Answer
Sealing crush washers create leak-tight fluid seals under compression on hydraulic fittings and automotive drain plugs, standardized under DIN 7603 (Form A solid copper/aluminum, Form C copper-asbestos/elastomer, and bonded Dowty seals).
Source: DIN 7603 Sealing Rings / ISO 1179 Hydraulic Port Connections · Last reviewed Aug 28, 2026
Specs
| Governing Standards | DIN 7603 Form A (Solid) / ISO 1179 / SAE J514 |
| M10 Sealing Washer (DIN 7603) | ID: 10.0 mm | OD: 14.0 mm | Thickness: 1.0 mm (Copper / Aluminum) |
| M12 Sealing Washer (Oil Drain Plug) | ID: 12.0 mm | OD: 16.0 mm to 18.0 mm | Thickness: 1.5 mm |
| M14 Sealing Washer (Standard Oil Drain) | ID: 14.0 mm | OD: 18.0 mm to 20.0 mm | Thickness: 1.5 mm |
| M16 Sealing Washer (Gearbox/Diff) | ID: 16.0 mm | OD: 22.0 mm | Thickness: 1.5 mm |
| M18 Sealing Washer | ID: 18.0 mm | OD: 24.0 mm | Thickness: 1.5 mm |
| M22 Sealing Washer | ID: 22.0 mm | OD: 27.0 mm | Thickness: 1.5 mm |
| Bonded Dowty Seal (Metal + NBR/FKM) | Steel outer ring with vulcanized inner trapezoidal elastomeric lip (Self-centering) |
| Plastic Yield Mechanism | Ductile copper/aluminum crushes plastically into machining micro-grooves upon torquing |
DIN 7603 Metric Sealing Ring Sizing Matrix
| Nominal Thread / Port Size | Inside Diameter (d_1) | Outside Diameter (d_2) | Standard Thickness (h) | Material Options | Common Automotive Application |
|---|---|---|---|---|---|
| M10 / 1/8" BSP | 10.2 mm | 14.0 mm | 1.0 mm | Solid Annealed Copper (Cu) | Brake caliper banjo bolts, turbo oil lines |
| M12 | 12.2 mm | 16.0 mm or 18.0 mm | 1.5 mm | Solid Aluminum (Al) / Copper | Toyota / Lexus oil pan drain plug |
| M14 | 14.2 mm | 18.0 mm or 20.0 mm | 1.5 mm | Crush Aluminum / Copper | Honda, VW, BMW, Ford engine oil drain |
| M16 | 16.2 mm | 20.0 mm or 22.0 mm | 1.5 mm | Solid Copper / Bonded Dowty | Manual transmission fill & drain plugs |
| M18 | 18.2 mm | 22.0 mm or 24.0 mm | 1.5 mm | Solid Aluminum / Copper | Differential drain plugs, diesel fuel lines |
| M20 | 20.2 mm | 24.0 mm or 26.0 mm | 1.5 mm | Solid Copper / Bonded Dowty | Heavy equipment hydraulic manifold ports |
| M22 | 22.2 mm | 27.0 mm | 1.5 mm | Solid Aluminum / Copper | Temperature sensor ports, oil coolers |
Why Crush Washers Must Never Be Reused
Sealing rings function through plastic deformation rather than elastic spring recovery:
- Work Hardening of Annealed Copper: New copper crush washers are fully annealed (dead soft). Under the first torque load (25–35 ft-lbs on an engine oil pan), the copper deforms into the micro-scratches of the aluminum pan surface. In doing so, the copper undergoes strain-hardening, making it rigid and brittle.
- Second-Use Leaks: Re-torquing a previously crushed washer requires significantly higher torque to deform the work-hardened metal, frequently stripping female aluminum oil pan threads before achieving a seal.