A drilling spool is a connector which allows choke and kill lines to be attached to the BOP stack. The spool must have a bore at least equal to the maximum bore of the uppermost casing spool. The spool must also be capable of withstanding the same pressures as the rest of the BOP stack (Figure 23). These days outlets for connection of choke and kill lines have been added to the BOP ram body and drilling spools are less frequently used. These outlets save space and reduce the number of connections and therefore potential leak paths.