Common hammer union seal materials include nitrile rubber (NBR), fluorocarbon (FKM/Viton), hydrogenated nitrile (HNBR), and perfluoroelastomer (FFKM) selected based on fluid compatibility and service conditions. Nitrile seals handle petroleum-based fluids and moderate temperatures economically. https://globalsealstech.com/product/hammer-union-seal-2/