This is a Blue Force Gear Mount, model UWL-625-BK.
The Universal Wire Loop is one of the most versatile sling attachment points made. A flexible nylon coated stainless steel wire allows for a sling attachment through eyelets" loops" slots" or any other opening that the wire fits through. The sling loop body is CNC machined from 6061-T6 aluminum billet before being tumbled and bead-blasted for a non-reflective surface. The loop is hard-coat anodized before the nylon coated stainless steel aircraft-grade cable is installed with ball-shank ends. The result is a sling adapter with limitless uses. Cable outer coating may deform if subjected to extreme barrel heat but the stainless core will not melt. Universal Wire Loops are quieter and stronger than traditional hook attachments and won't wear through eyelets.
Features:
Do not install UWLs around the buffer tube of M4s as this may interfere with the operation of the charging handle