Depends upon the sling, which depends upon weapon and era.
Worst one to use as a first-go: The US M-1905 leather sling. This sling was a a marvel of straps and hooks, and gave excellent support for rifle marksmanship. It's not a friend to modelers; even the full-size variant needs a diagram or two to sort out. These were used on M-1903 & 03A3, the M1 Garand, and even (a slight) few P-17 rifles. A lengthened version was on the BAR.
By 1943, the leather sling was being replaces by cloth webbing sling. This looped back on itself fore and aft. It was used on almost all US shoulder weapons, including the Bazooka.
The other US cloth cling was simple as spit. The M-1 Carbine sling had a tiny loop that fit around a standard oiler, passed through the stock, then around the sling loop to fasten with a snap fastener.
That fabric Garand sling was used on the M-14, and a version rode on the M-16.