The one I have looks like a buttstock but the end splits into two thick "flaps" which cradle across the top of the arm, basically aligning your forearm with the tube through the brace. There's a strap that wraps around the bottom of the arm, and it locks the weapon in place. They were originally made for disabled veterans who needed an ability to shoot with accuracy if their limbs were compromised in any way. You can actually use them to shoot very accurately, but they're not designed as a shoulder stock (although they could technically be used as such).