This is a Sig Sauer Stabilizing Brace known as the PCB, model PCB-X-FOLD-BLK.
Side-Folding Brace for Sig MPX/MCX
Features:
1913 Picatinny Mount
This is a Sig Sauer Stabilizing Brace known as the PCB, model PCB-X-FOLD-BLK.
Side-Folding Brace for Sig MPX/MCX
Features:
1913 Picatinny Mount