Garand Thumb features Geissele URGI AR-15 upper receiver in this video. The URGI stands for the "Upper Receiver Group Improved" that is now being introducted into service at the United States Army Special Operations Commans (USASOC) and has improvements over the standard Mil-Spec M4 upper. The Giessele URGI is a "near clone" of that URGI of the USASOC according to Brownells.