1. Quality certificate: ROHS. 2. Materials: NBR, NR, FPM...etc 3. Use for all machines,size:50-630 SR:good resilience,ozone resistance, ageing resistance, low temprature and bending resistance,low compression deformation,perfect electrical performance.SBR: high tensile strengh,abrasion resistance,heat resistance,ozone resistance,acid resistance,alkali resistance,alkali resistance,good flex ...