90A Durometer Urethane Back-Up Rings -334 Dash Size, Per Pack

Urethane has a natural elasticity to it, so you can stretch the ring enough to get it seated without fighting it. Once it's in place, the material returns to its molded dimensions pretty quickly. That recovery is actually what makes urethane a good choice here, you get a secure fit without needing tools or heat to work it into position. The 90A durometer keeps it firm enough to resist extrusion under pressure while still being flexible enough to install by hand.

Sizes on these back-up rings correspond to O-ring sizes, so a -334 back-up ring is meant to pair with a -334 O-ring size.

That's how they work. The urethane is molded at 90A durometer, which gives it enough flex to stretch over whatever you're fitting it onto, then it pulls back to its original shape pretty quick. Makes the whole installation a lot less of a hassle than you'd expect for a ring this firm.

For these, the sizes correspond to O-ring sizes, so a -334 back-up ring is meant to match a -334 O-ring size.

Sizes for these rings correspond directly to O-ring dash sizes, so this -334 will match the appropriate O-ring.