Ace O-rings, silicone 

Viton® A linear copolymer of vinylidene fluoride and hexafluoropropylene; good chemical resistance
Silicone Elastomer with high-temperature and ozone resistance
FETFE® Fluoroelastomer with TFE additives and high chemical resistance
CAPFE A resilient rubber core encapsulated in nonporous FEP
O-ring measurement
1. Measure the I.D. and wall thickness (mm) of the existing O-ring.
2. Locate a replacement in the tables that follow.
3. Ace Glass part numbers are provided for convenience.