This is the Magpul MOE Sling Attachment QD for Magpul MOE hand guard and forends. 

It provides a forward sling attachment point for push-button QD slings such as the MS4 GEN 2.

The MSA QD is case-hardened and made from Melonite™ finished steel for wear and corrosion resistance. Its anti-rotation feature prevents swivels from spinning. 

Made in the USA.