Manufacturers suggested name is seat ring; material is stainless steel with stellite
NSN 5910-01-412-0709
NSN 5925-01-291-1525
NSN 6645-01-590-6385
NSN 5975-00-688-4625
NSN 6220-01-238-2632
NSN 5950-01-276-7180
NSN 6650-00-105-1418
NSN 4140-01-451-9841
NSN 5990-00-362-1453
NSN 6220-01-514-0381
NSN 6220-00-266-8222
NSN 5999-01-126-2195