Device used to apply torque to the drill string during drilling and normally located in the centre of the drill floor. NOTE Can be rotated and can support wear bushing or spider.
Source: API RP 17G, Recommended Practice for Completion/Workover Risers, Second Edition, July 2006 (Reaffirmed April 2011). Global Standards
A device through which passes the bit and drill string and that transmits rotational action to the kelly.
Source: API RP 59, Recommended Practice for Well Control Operations, Second Edition, May 2006. Global Standards
Source: API RP 64, Recommended Practice for Diverter Systems Equipment and Operations, Second Edition, November 2001 (March 1, 2007). Global Standards