This is an optional Traxxas Propeller Shaft, and is intended for use with the Traxxas Villain EX and Blast boats. The 1529X prop shaft allows the use of optional non-metric 3/16" inner diameter props on Traxxas boats. Typical aftermarket props from manufacturers such as Octura, Graupner, and Prather use the standard 3/16 thread size. Two of these are required for the Villain EX.