Bonded Seals & Bonded Washers

Bonded seals — also called bonded washers, Dowty seals, or self-centering seals — consist of a metal washer (typically steel or stainless steel) with an elastomer sealing ring bonded to one face. When the bolt or stud is tightened, the elastomer compresses between the washer and the mating surface, sealing the connection against internal pressure and external contamination. Bonded seals are used on static bolted joints: hydraulic pump and motor mounting flanges, gearbox inspection covers, fuel and oil line banjo connections, pipe flanges with limited groove space, and any through-bolt port where a conventional O-ring groove is impractical. They center on the bolt shank, which simplifies assembly compared to loose O-rings on large bolt circles. The metal washer provides mechanical support and limits elastomer extrusion under high bolt preload. The bonded ring is typically NBR for oil and fuel, FKM for high temperature and chemicals, or EPDM for water and outdoor exposure. Self-centering types include a locating lip on the inner diameter; plain types rely on bolt alignment. Installation requires controlled torque per bolt size and grade. Over-torque crushes the elastomer; under-torque leaves the joint under-sealed. Replace bonded seals at every disassembly — reused seals take permanent set and often leak on reassembly. We supply metric and imperial bonded seals in standard and stainless steel washers. Custom inner/outer diameter and elastomer grade available from drawing. MOQ from 10 pieces on standard sizes, 1 piece on custom prototypes.