The ARC Splined Alloy Crank utilizes a 10 tooth straight sided spline that creates a much greater load dispersion area than a normal keyed crank. No more broken PTO shafts and makes clutch removal a breeze. A must for today's high horsepower Junior Dragsters. CNC machined toughest material ever used for small 4 stroke engines. Features a true 1/8" journal radius for strength and durability. Also features airplane wing style counter weights that are proportionally designed for superior balance. The #6598 crankshaft was designed for aftermarket flathead blocks that have extra spacing between the crank and cam. Will not fit the Briggs Raptor and Blockzilla blocks. Requires splined clutch post and large gear set.