Abstract: A torque-limiting coupling having two co-axial rotary members interconnected by one or more shear pins extending between two fixing blocks detachably secured one to each of the two rotary members. Each shear pin is firmly secured in bores in the two blocks, and each block is firmly secured by two screws onto a chordal flat on the periphery of each rotary member, so that, in the event of a pin being sheared, the blocks with the broken pin can be removed radially and then replaced with another pin. In a coupling having two or more pins the shear load is distributed equally between the pins. Each pin may be bonded in the bores in the fixing blocks. Alternatively, each pin may be a loose fit in the bores and the block dimensioned so that when it is screwed firmly onto its chordal flat the block is flexed or deformed so as to reduce the diameter of the bore and thereby clamp the shear pin firmly in the bore.