A large, spool-shaped metal pipe that is used between the preventer elements on a BOP stack to attach choke and kill lines. The choke lines and kill lines can attach to one spool or two spools with a blowout preventer in between. The spool can be studded, flanged, or clamp-on connected.
Depending on expected pressures, a combination of one annular preventer, one or more ram-type preventers and a drilling spool can be used as wellhead control equipment.