These Swagelok® 1/4" Male NPT pipe plugs are made of corrosion resistant 316 stainless sheel and are part number SS-4-P. They are designed to seal unused female NPT ports in our KF-to-NPT Female adapters or other open 1/4 inch NPT ports in your vacuum system. . 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.