Designed with competitor safety in mind Hegar offers the 50mm axle sprag assembly. Engine lock up followed by axle lock up from mechanical failure can be common with direct drive engagement motor packages like shifter karts. Installing the Hegar sprag protect against that threat keeping the driver and others around safer. The Sprag allows the kart to simply coast to a stop after drive failure. Better overall handling and zero load on the motor under braking by removing all compression braking also improves engine life and decreases damage to the cylinder after seizure or transmission failure. Comes complete with 1 lock collar, 1 spacer for bearing side spacing, 1 wrench for drive gear tightening and one can of Silkolene Pro lube which is the only lube to be used with this unit. Using other lubes can cause slip or part failure. 428 sprockets only, sold separately. Sometimes this site can be slow to respond so please call us to order! 503-659-1234 M-F 8am-4pm Pacific Standard time