A series of projections and slots used instead of a key to prevent relative rotation of cylindrically fitted machine parts. Splines are several projections machined on the shaft; the shaft fits into a mating bore called a spline fitting. Splines are made in two forms, square and involute (see illus.). Since there are several projections (integral keys) to share the force in transmitting power, the splines can be shallow, thereby not weakening the shaft as much as a standard key.