Leica 13352 Swing-Out Polarizer made to fit Leica M lenses with a 39mm filter thread. It does not thread in but clamps onto the outside of the lens front ring. Swing it in front of the viewfinder and adjust for the desired effect and then swing it 180 degrees over the lens and it holds the setting. Makes a huge difference in scenics. This is in really good condition, physically, cosmetically and glass, all good.