Cooper T red velocity adjustable Rear asa in good shape but has a couple dings. Does not screw in from the top, has to screw in from the base. I had it on a Taso Spartan and the grip frame of the spartan was drilled out to allow a 10x32 screw through. Uses 2 holes in asa. One for air inlet and one for allen adjustable screw. If you use this on a nelspot frame you might need to drill your back grip frame hole out. I've only come across a couple of these, I have one on my maximaster. Easily adjust velocity, Screw in for more tension on valve body screw and lower velocity or screw out for less tension and more velocity.