Rollers that prevent the lifting of the revolving upper-structure from the roller path. Hook rollers are a means to connect the upper-structure to the foundation or pedestal.
Source: API RP 2D, Operation and Maintenance of Offshore Cranes, Sixth Edition, May 2007. Global Standards
A means to connect the upper structure to the foundation or pedestal by using rollers to prevent the revolving upper structure from toppling.
Source: API RP 2D, Operation and Maintenance of Offshore Cranes, Seventh Edition, December 2014. Global Standards