Subclass 1/091: Couplings for rigidly connecting two coaxial shafts or other movable machine elements (for attachment of cranks to their shafts F16C 3/1 ) for attachment of a member on a shaft or on a shaft-end (attachment of marine propellers on shafts B63H 23/34) with clamping hub; with hub and longitudinal key with radial clamping due to axial loading of at least one pair of conical surfaces and comprising a chamber including a tapered piston moved axially by fluid pressure to effect clamping