With helical gearing the teeth mesh gradually and at no period is the full width of any one tooth completely engaged. This gradual engagement and release of the teeth eliminates much of the shock and jar associated with straight spur gear teeth when operating under heavy loads. The shaft support bearing design has to be more substantial than a spur gear drive because of the end load produced when in operation. The load is in opposite directions from one shaft to the next in a helical gear combination or train of gears. Single helical gears are mainly mounted on parallel shafts but can be mounted on shafts at 90 degrees to each other (as you would find in a worm and wheel shaft arrangement) or at any angle between 0 and 90 degrees. These gears are sometimes known as spiral or skew helical gears.