The GRS Heavy Duty Flush Cup Base is a pair of threaded, all-steel sling mounting bases designed for exceptional strength and security. These bases are precision-engineered to accept any Grovtec push-button swivel and can be added to any synthetic or wood stock to create multiple high-strength swivel positions. They are standard components used on GRS's rugged composite models, including the Bifrost, Fenris, and Ragnarok. Finished with a non-glare black oxide coating, these bases offer a low-profile, flush-mounted solution for heavy-duty sling or bipod attachment in extreme field conditions.