The Sentry 4S-CS Seal Assembly is a secondary seal assembly that features both O.D. and I.D. seals. It consists of reducer bushing body, (2) CS Seals in the I.D. of the bushing accompanied by (2) S-Seals on the O.D. A single snap ring also retains the bushing in the secondary seal area of a casing spool or tubing head.