Boston Gear change gears are used primarily on machine tools to provide different cutting speeds while using a constant speed input. All Boston Gear change gears are manufactured with a double key to accept the compound steel bushings that connect two gears together, allowing them to spin on an intermediate shaft. The change gears we stock range from 20-tooth through 128-tooth gears, in one tooth increments, depending upon the diametrical pitch, for a nearly infinite number of ratio possibilities. Be sure to ask for the Boston Gear compound steel bushings designed specifically for use with these gears. Specifications Material: Steel KWY/Setscrew/Other: W/ Double KWY Only Pressure Angle: 14-1/2 Degrees Documentation Catalog Product Section Engineering Data Full Catalog ISO Certificate