Design Factor is the ratio between the minimum Break Strength of a new assembly and the Rated Capacities/Working Load Limits. In the U.S. and Canada, the industry standard design factor for web slings, round slings, wire rope and wire mesh slings is 5:1. For chain slings, it is 4:1. Tow straps and tie downs have a 3:1 design factor. Never use slings or tie downs in excess of their rated capacities/working load limits.