Worms and worm gears are used to power right angle, non-intersecting shafts. In normal applications the worm gear is driven by the worm. The most popular use of worms and worm gears is in applications where high ratio speed reduction is desired in a relatively limited space. They are also used in applications where high resistance to the worm gear shaft reversing and driving back through the worm is desired. Martin Worm Gear, Plain Reborable, 0.5 to 0.626 in Bore Dia, 1.69 in Outside Dia, 18:1 Gear Ratio, 1 Number of Threads, 18 Teeth, 12 Diametral Pitch, 1-1/2 in, 1/2 in Face Width, Right Hand Direction of Rotation, Type B, 1-1/4 in Hub Dia, 5/8 in Hub Projection, 14.5 deg Pressure Angle, 1/8 x 1/16 in Keyway, Cast Iron