HDA3 Stock and Brace for MP5K, SP5K

The HDA3 is a modular, USA-made stock and brace system developed by Haga Defense and A3 Industries. Built for strength, adaptability, and cross-platform compatibility, it delivers premium rigidity, smooth adjustability, and long-term durability without compromising aesthetics.

Features:

• Heavy-duty steel hinge with solid lockup when open or folded. Folds left at a 3.5° cant.
• All-metal internals for durability, including an aluminum cheek-riser button and length-adjustment latch tied into an extruded aluminum spine.
• Offered as a stock with molded extension and textured Santoprene buttpad, or as a brace-ready model designed to accept multiple 1.195" tube-style arm braces.
• Seven length positions in 0.5" increments and a three-position cheek riser (0, +0.25", +0.50").

Specifications:

• Made in the USA
• 6061 hard-coat anodized aluminum adapter
• Adapter dimensions: 2.85" H × 1.64" W
• Includes rubber buffer
• Stock length: 7.93"–10.93"
• Brace mount length: 8.26"–11.26" (without brace installed)
• Stock weight: 1 lb 5.0 oz
• Brace mount weight: 1 lb 3.5 oz
• Nitride-coated 17-4 stainless steel, left-folding hinge
• Extension: 7-position 6061 aluminum extrusion with 7075 locking latch
• Cheek riser: 3-position polymer riser with anodized aluminum adjustment button
• Polymer components: 30% glass-fiber reinforced nylon
• Textured Santoprene TPE buttpad (stock only)
• Sling mounts: rear sling loop, two steel QD points, one QD point on the adapter

Compatible With:

• MP5K, SP5K
• In-spec clones and custom builds