A power take off coupling for connecting an engine (20, 21) to a site accessory (16, 14, 17), comprises a resilient power transmission component (3) within the coupling; a latching device (8, 46, 9) to mechanically latch the accessory to the engine (20, 21), with a manually operable release handle (13) to effect unlatching. A power output shaft of the engine (20, 21) carries one half (5) of a dog clutch with the other half (7) carried by the accessory (16, 14, 17). An alignment arrangement comprises a first annulus ring (18) attached coaxially to an output shaft assembly of the engine (20, 21), and a second annulus ring (19) attached coaxially to an input shaft assembly of the accessory, with the two rings (18, 19) being of different diameters, such that one ring is adapted to be engaged coaxially within the other ring with close tolerances, such that the external periphery of the smaller ring (18) engages at least parts of the internal periphery of the larger ring (19) to provide for accurate coaxial alignment of the power output shaft of the engine (20, 21) and the power input shaft of the accessory.