Pinion gears are available to fit Big Twin engines from 1937 thru 1989. These high quality gears are carefully machined, heat-treated and then finish ground. If the stock gear is unmarked and the size is unknown we recommend that you order a gear in the middle of the tolerance range. These sizes were used more often and should provide adequate gear clearance under most circumstances. Note: Gear sizes for 1954 thru 1989 are listed from biggest to smallest. This color coding sequence is identical to stock Harley-Davidson color coding for the late 1977 thru 1989 models. For the 1954 thru early 1977 models there was only one size available from Harley-Davidson, Jims and S&S issued their own color coding for these pinion gears. Sizes are given measured over .105" pins.