Chicopee, and boo1, thanks for your comments.
In Britain we have BS1290, 'Wire rope slings and sling legs for general lifting purposes'.
I work in the offshore industry in Britain, and have not got access to American codes.
I am writing a spreadsheet that designs 4 leg slings to all the common codes i.e. DNV Marine Operations, DNV Offshore Containers, BS1290 e.t.c., and would also like to include the standard American design procedure. There must be one commonly recognised standard in the USA, that gives guidance on the design, proof testing, identification stamping, and certification, of a 4 leg sling ?
If so could someone give me the name of this specific code, and the reference sections ?