Abstract: A helicopter rotor includes attachment means for attaching a rotor hub to a tubular rotor drive shaft in a manner establishing a primary thrust load path and further attachment means adapted to provide a normally passive secondary thrust load path and operative automatically to retain the rotor hub in the event of a failure in the primary thrust load path. In the described embodiments the further attachment means comprise a multi-part collet consisting of a plurality of identical collet parts located internally of the drive shaft. Each collet part has an external frusto-conical surface one end for location adjacent a mating surface formed internally of the drive shaft, and a radially extending flange portion at its other end for attachment to an end surface of the drive shaft.