here is a side sling adapter. I pulled it off a new colt M4 barrel many years ago, it is the USGI version... not one of those cheapo copies made in china. nice thick rubberizing on the swivel. both roll pins are the heavy duty dual coil type. the swivel rivot is factory installed.
priced at $29 + $3.50 s/h. pmt by postal money order or PP gift. will ship promptly via tracked USPS upon receipt of pmt.