The Wing Traveling Pulley makes a great building block for your own homemade system. The Wing comes from longtime Italian climbing-gear manufacturer C.A.M.P., and boasts a cool quick-release mechanism. To attach it to the zipline, you pivot the arm out and snap it on. When you’re in the air, it’s impossible to detach from the zipline. The device has a maximum speed of 45 miles per hour, weighs 11.9 ounces, and can handle cables as thick as 15/16 of an inch.