Up for sale is a 3 position adjustable stock for  Gen 3 or older, compact models. I don't believe it fits Gen 4 or newer, but feel free to independently verify. I took it in a trade, with the intent of buying an older Glock, and registering as SBR, but never ended up making the leap. That being said, ALL NFA RULES APPLY! None of my business what you do with it afterwards, but installing this WILL make your pistol a short barreled rifle in the eyes of the law.