The Leica filters for the Leica M system are made of optically pure glass, parallel plane ground and precisely annealed, so the full performance of the Leica M lenses is retained even with a filter attached. The range is purposely limited to the filters most commonly needed in photographic practice
A characteristic of polarization filters is that they show the same effect after each 180-degree rotation. The polarization filter for the Leica M is thus supplied with an adapter with a swivel fitting, allowing it to be rotated 180 degrees to in front of the viewfinder so you can assess and control its effect before taking the shot.
There are two threaded adapter rings supplied in filter sizes 39mm and 46mm. These rings will enable the use of the Universal Polarizing Filter-M with the majority of the present interchangeable lenses in the M-system lineup.