... all available. Description of Aging-proof Flat O-ring with High Quality:1. Materials: can be NR flat o-ring, HNBR, Buna, FVMQ ... , MVQ, ACM, FLS, CR, SBR, SI, BR, IR, EPDM, IIR, butyl, PU, E/A ... flat o-ring. 3. Hardness: 30~90 shore A or IRHD as your request, tolerance is ± 5 shore A, and can be ±3 shore A ...