ISC Medium Rigging Pulley for up to 20mm Rope - MBS 300kNISC Medium Rigging Pulley for up to 20mm Rope 300kN Part of the new ISC 200 Series.. The next generation ISC Rigging Pulleys are up to 150% stronger than the equivalent ISC standard Rigging Pulley models. The new low profile Springlock mechanism features a new Safelock locking button to offer further security and ease of use. Simply push the Safelock button and turn the axle head 180 to the release position. The Safelock button can be depressed and