This is the Lima Six ar-15 nutsack adapter. This goes into a tradition ar-15 magwell, locks securely into place, and allows the use of the nutsack at the correct feed angle. Verified and approved by Lima Six themselves. 
 
These products are all made right here in The USA!
 
Please note that due to the nature of 3D printing, minor imperfections may be present. However, we stand behind the quality of our products—if it breaks, we’ll send you a replacement, no questions asked.