Ditto what these guys said, except I couldn't get mine back into my ATI stock, the hole is too small. Funny enough, I only discovered that spring after having already taken the gun apart and put it back together a few times after installing the aftermarket stock (didn't pay enough attention when replacing the stock in the first place I guess). IMO that spring really isn't all that important, my trigger group comes out fine without it, so I've just left it in the wood stock.