A power take off coupling for connecting a power unit to a site accessory (16, 14, 17), comprising (i) a resilient power transmission component within the coupling; (ii) a latching device (9, 10, 49, 50) to mechanically latch the accessory (16, 14, 17) to the power unit, with a manually operable release means operable when unlatching is required, wherein the latching device (9, 10, 49, 50) comprises a latching plate having a coaxial and rotatable disc biased by springs to a closure position; (iii) a power output shaft of the power unit carrying one half of a dog clutch with the other half carried by the accessory (16, 14, 17) to be driven; and (iv) a power unit to site accessory (16, 14, 17) alignment arrangement comprising a first annulus ring attached coaxially to an output shaft of the power unit, and a second annulus ring attached coaxially to an input shaft of the accessory (16, 14, 17) to be driven, with the two rings (18, 19) being of different diameters such that one annulus ring is adapted to be engaged coaxially within the other annulus ring with close tolerances, such that the external periphery of the smaller diameter annulus ring engages at least parts of the internal periphery of the larger diameter annulus ring to provide for accurate coaxial alignment of the power output shaft of the power unit and the power input shaft of the accessory (16, 14, 17), characterised in that a leading edge of the larger diameter annulus ring is chamfered to assist initial engagement, and in that the latching device (9, 10, 49, 50) comprises three mounting holes provided in the latching plate for mating engagement with three corresponding projections on the accessory (16, 14, 17), with lead-in surfaces between the mounting holes and the projections to ensure both ease of engagement and accurate alignment, wherein each projection comprises an enlarged head with a pilot, lead-in nose, with a neck portion behind the head, wherein the neck portion of each projection is engaged by a spring biased, and radially displaceable lever carried by the coaxial and rotatable disc for mounting on the power unit. (i) a resilient power transmission component within the coupling; (ii) a latching device (9, 10, 49, 50) to mechanically latch the accessory (16, 14, 17) to the power unit, with a manually operable release means operable when unlatching is required, wherein the latching device (9, 10, 49, 50) comprises a latching plate having a coaxial and rotatable disc biased by springs to a closure position; (iii) a power output shaft of the power unit carrying one half of a dog clutch with the other half carried by the accessory (16, 14, 17) to be driven; and (iv) a power unit to site accessory (16, 14, 17) alignment arrangement comprising a first annulus ring attached coaxially to an output shaft of the power unit, and a second annulus ring attached coaxially to an input shaft of the accessory (16, 14, 17) to be driven, with the two rings (18, 19) being of different diameters such that one annulus ring is adapted to be engaged coaxially within the other annulus ring with close tolerances, such that the external periphery of the smaller diameter annulus ring engages at least parts of the internal periphery of the larger diameter annulus ring to provide for accurate coaxial alignment of the power output shaft of the power unit and the power input shaft of the accessory (16, 14, 17),