The SR-71 cable pulley represents the most advanced design work using state of the art engineering techniques to build the safest and finest trolley for the ropes course industry. The 304 stainless steel frame is .101 thick for superior strength and trouble free use. Unlike the competition it is assembled using machined 304 stainless axles which may cost more but gives the SR-71 unparalleled structural integrity. Safety is always a primary objective and the SR-71 uses an additional back-up axle should there be a catastrophic failure of the sheaves during use. This third axle also gives the SR-71 superior stability. The sheaves are 2" in diameter and case hardened to 56-58 Rockwell and ride on sealed ball bearings to provide excellent wear characteristics in challenging outdoor environments. Built for 3/8" and 1/2" diameter cable. Independent test rated to 19,000 lbs /84kn. Exceeds A.N.S.I., OSHA, and NFPA class G standards.