This is a SB Tactical Stabilizing Brace known as the SBT, model SBT-01-SB.
The SBT Pistol Stabilizing Brace was inspired by the iconic B&T design for HK platforms. Featuring an integral" side-folding mechanism" the SBT fits the B&T APC and HK UMP pistols.
Features:
Fits HK UMP and B&T APC
Includes complete assembly, adjustable nylon strap
Ready to install