Helical Gears are similar to the spur gears except that the teeth are at an angle to the shaft ,rather than parallel to it as in a spur gear .The regulting teeth are longer than the teeth on a spr gear of equivalent pitch diameter .The longer teeth caused helical egars to have he following difference from spur gears of the same size .

Tooth strength is greater because of the teeth are longer

Great surface contact on the teeth allows a helical gear to carry more load than a spur gear

The longer surface of contact reducers the efficientcy of a helical gear relative to a spur gear .