An industry standard value in prusik minding crevasse rescue pulleys from SMC.  Prusik minding pulleys like these simplify crevasse rescue setups and help keep prusik knots from becoming jammed in your pulleys while hauling. Every climber roping up for glacier travel should carry at least one of these on their harness ready to use.  The rotating aluminum side plates make this pulley very easy to put on and take off of the rope. The flatter edges of the pulley side plates opposite the carabiner attachment holes tend prusik knots to help keep them from jamming in the sides of the pulley in between the sheave and the carabiner.