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The FS-Seal has been designed to seal against rough casing in which wide tolerances and varying surface finishes create difficult sealing conditions. Utilized as a large cross-section interference seal to bridge large extrusion gaps associated with sealing on rough mill casing, the specialized FS-seal bump provides higher sealing contact stresses, while the curved recess on the back of the seal controls the amount of compression (squeeze) on the seal element by allowing it to deflect outward when sealing against a larger-than-normal outer-casing diameter or an out-of-round section of casing. Supplied integral to a casing head bottom preparation as a 1-FS (one seal with no secondary) or 2-FS (two seals with one secondary) packoff, this seal can also be supplied as a separate 4-S packoff bushing, which incorporates a secondary S-Seal on the bushing OD and a secondary FS-Seal on the ID. The FS-Seal is available for 4" to 30" pipe sizes. It is rated to 10,000 psi working pressure and a 0° to 250°F temperature range for sizes up to 16", while the larger sizes are rated to 5,000 psi working pressure.