GrovTec base cup accepts QD sling swivel. The GrovTec base cup can be threaded into the side cup holes on all MBA buttstocks (MBA-1 MBA-2 MBA-3 and MBA-4). Each buttstock has a side cup hole on both sides of the buttstock frame. The cup can be installed with an separately available installation tool or a 1/4″ Allen wrench. We also have a the QD swivels and complete kits available. See the install Tech Tip video in the Sling Swivel tab.