These Swagelok® Male NPT (MNPT) tees are made of 316 stainless sheel and are part number SS-4-MT. They are used to make vacuum connections between three Female National Pipe Thread (FNPT) fittings. For a good vacuum seal we always recommend using a pipe thread sealant when assembling tapered threads. Pipe thread sealants and pipe tape are sold on this web site.