Manufacturers suggested name is seat ring; material is stainless steel with stellite
NSN 6645-00-998-2918
NSN 5960-01-495-0859
NSN 6150-01-433-2692
NSN 5925-01-143-2453
NSN 5930-00-422-1188
NSN 6220-01-273-7424
NSN 5855-00-237-4088
NSN 6105-01-620-4471
NSN 6685-01-041-4407
NSN 5965-01-621-3467
NSN 6685-01-387-9084
NSN 5996-00-605-0397