I have one. Love it. Great shooter. Be aware it is NOT parts compatible with a ar. The mags are not either. IE you can not use Black dog mags or other ar 22lr mags in it. Light accurate and great performer.
You need a long tube it is a four post pattern shown in the close up. The nut is inside the handgaurd way in there. I made this wrench for mine as I have to remove the barrel to put it in my lathe for threading.