The spline has an inner (4) and an outer (2) spline which grip in each other. The inner spline in the shape of a semicircular groove has a preset radius. The outer spline is shaped so that its two sides are curved over a certain length with the same curvature as the inner spline. The distance between the two sides of the outer spline is less than that between the two sides of the inner spline. The top of the outer spline has a flat part with a pre-set length.
