A3 Industries HDA3 Universal 1913 Folding Brace

The A3 Industries HDA3 Universal 1913 is the premium universal-mount version of the platform-specific HDA3 braces (Kuna, Scorpion, Bren 2). It runs a steel hinge assembly with all-metal internals for the lockup mechanism, mated to a 30% glass-fiber-reinforced nylon body. Length adjusts in 0.5-inch increments across 7 positions, and the cheek riser has 3 height stops (flush, +0.25 inch, +0.50 inch) for shooters running magnified optics.

The brace folds to the left side at a 3.5-degree downward cant, which clears the ejection port and most optics when stowed. Two HD steel quick-disconnect (QD) sockets sit on either side of the body for ambidextrous sling routing. Both the LOP and cheek-riser adjustments can be operated one-handed without tools.

Mount the HDA3 on any host with a 1913 Picatinny rear interface: Springfield Kuna, Stribog with factory 1913 adapter, Scorpion with HBI 1913 adapter, Sig MPX/MCX, Bren 2 with 1913 adapter, B&T APC9 and GHM9, AR pistols with 1913 endplates. Right-side folding variants are listed as future SKUs but were not shipping at the time of this guide. The HDA3 is the most adjustable 1913 brace currently on the market and is the answer for shooters who want stock-level adjustability while keeping a pistol-configured firearm.