When used with worm gears, Boston Gear® worms provide an effective answer for power transmission applications requiring high ratio speed reduction in a limited space using right angle (90 deg), non-intersecting shafts. Manufactured from acetal, nylon and hardened and unhardened steel, they offer the smoothest, quietest form of gearing when properly applied. Because the efficiency of a worm gear drive depends on the lead angle and number of starts on the worm, it's important to keep the ratio as low as possible. It is equally important that worms and worm gears used together must have the same diametrical pitch and threads. Boston Gear® Helical Gear Worm, Spiral Tooth, 1/2 in Bore, 1.17 in OD, 4 Threads, 12 Diametral Pitch, 1 in Pitch Diameter, 1-1/8 in Face Width, 18 deg 26 min Lead Angle, Right Hand Direction of Rotation, 3/4 in Diameter Hub, 0.38 in Hub Projection, 1.505 in Overall Length, 14.5 deg Pressure Angle, Steel