90A Durometer Urethane Back-Up Rings -228 Dash Size, Per Pack

Sizes line up with standard O-ring dash sizes, so a -228 back-up ring corresponds to a -228 O-ring size.

Urethane construction at 90A durometer gives these rings enough flexibility to stretch during installation, then they return to their original dimensions on their own. No special tools or coaxing required. That's actually one of the practical advantages of urethane over harder materials for this type of application.

Urethane at 90A durometer has enough flex to stretch over a groove without taking a set, and these are molded specifically to return to their original dimensions after installation. The -228 dash size follows standard O-ring sizing, so as long as your groove matches that designation, seating them is pretty straightforward. Once they're in place, the material holds its form and does its job resisting extrusion under pressure.