RBS has found these to be some of the strongest and well built blower gear bolts on the market. These are made from billet heat treated steel and the washer has been built into the bolt head while having the mating surface ground for perfect parallelism. These are designed to be used with 3-71 thru 16-71 blowers that use a 1.125" shaft with a 1/2-20" thread. The bolt dimensions are 1/2-20" x 1.00" x 1.395" flange. THESE WILL NOT WORK WITH KOBELCO BLOWERS OR BLOWERS THAT USE A 1.250 GEAR REGISTER.