Spur gears have straight teeth, and are mounted on parallel shafts. Spur gears are the simplest and most common type of gear. Their general form is a cylinder or disk. The teeth project radially, and with these “straight-cut gears”, the leading edges of the teeth are aligned parallel to the axis of rotation. These gears can only mesh correctly if they are fitted to parallel axles. Spur gears on non-parallel shafts can mesh, but only point contact will be achieved, not line contact across the full width of the tooth; also the length of the path of contact may be too short.