... Table E4. Disc: Grey iron, Ductile iron, with or without EPDM5. Seat: Stainless steel, Brass/Bronze etc6. Testing: API 598, ISO 52087 ... steelDisc Grey iron, Ductile iron, Carbon steel, Stainless steel, with or without EPDMSeatEPDM / NBR / VITON / PTFEStemStainless steel, Brass/Bronze etc BushingPTFE"O" ringNBR, PTFELevelMalleable ...