Just found this one online, i was going to use a safety factor anyway, given this 1.5 rating I may increase my safety factor
http://www.wireworld.com/amefird/selectingspi.pdfHaving read the information and done some more searching ( It helps of you use the correct terms when doing a search "DUUHHH!" ) all of my slings and tie-downs have huge safety margins, a flat-tack is immensely strong.