n: a heavy, flanged steel fitting connected to the first string of casing. It provides a housing for slips and packing assemblies, allows suspension of intermediate and production strings of casing, and supplies the means for the annulus to be sealed off. Also called a casing spool.

The portion of the casing that protrudes above the surface and to which control valves and flow pipes are attached.

a flanged steel fitting connected to the first string of casing. It allows suspension of intermediate and production strings of casing and is the means for sealing off the annulus.

The top of the first string of casing set in a well. Usually a heavy, flanged steel fitting which provides a means to attach various fittings or assemblies.