Use straight angled sides for generating spur and helical gears of maximum accuracy on gear hobbing machines Hobs are generally supplied with bore keyway however hobs with end drive slot can also be had on request Single & multistart hobs are designed to suit specific customer's requirement for pre-shaving & pre-grinding gears with profile features like protuberance & semitopping. Normally, accuracy classes are 'A', 'B' & 'C' as per DIN 3968.