A gear used to drive printing press rollers or cylinders in which the teeth are cut parallel to the surface of the cylinder. Spur gears on offset press printing unit cylinders are commonly found more often on older machines, having been replaced on newer presses by helical gears. Spur gears generally require the addition of a second gear, called a backlash gear, so as to reduce play, the unimpeded (and undesirable) lateral movement between gears. Helical gears by design reduce play. Cylinders in which the bearers (metal rings attached to the ends of the cylinder) of the plate cylinder run in contact with those of the blanket cylinder commonly use spur gears, while those that run out of contact use helical gears to reduce play and provide a smoother drive. (See Plate Cylinder, Blanket Cylinder and Helical Gear.)
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