A shaft coupling with a flexible annular sleeve, a driver end piece, and a driven end piece. The end pieces have a plurality of axially projecting prongs arranged so that the driver prongs loosely interlock in the spaces between the driven prongs with a gap between each pair of prongs. The sleeve fits snugly around the periphery of the loosely interlocked prongs. Each prong has at least one prong groove in its outer periphery. Each of two peripheral edges may be shaped to form a groove flank, and each set of two adjacent groove flanks on adjacent prongs may form a gap groove. The sleeve has a plurality of inner teeth including a plurality of groove teeth in alternating arrangement with a plurality of gap teeth. The prong grooves and groove teeth mesh, and the gap grooves and gap teeth mesh. Groove teeth may be bigger than gap teeth.