Pair of gear in mesh Cam and follower Generally, a higher pair is a constraint that requires a curve or surface in the moving body to maintain contact with a curve or surface in the fixed body. For example, the contact between a cam and its follower is a higher pair called a cam joint. Similarly, the contact between the involute curves that form the meshing teeth of two gears are cam joints, as is a wheel rolling on a surface. It has a point or line contact. Ball or spherical joint requires that a point in the moving body maintain contact with a point in the fixed body. This joint has three degrees of freedom.