Go here for more information on Leica M filter sizes...


http://www.imx.nl/photosite/leica/overview/listm.html


Series filters are unthreaded. They require a threaded ring to attach them to a lens. A series 7 filter retaining ring has 48x.075 threads so an E48 filter can be used in place of the Series 7 filter plus ring. A Series 8 filter uses a 60mm retaining ring so an E60 filter can be used in it's place. The E (I believe) stands for the filter thread pitch (0.75). The older Leica M lenses take a 39mm filter but I think the thread pitch is not the same as the E thread. I think the old 39mm ones had a pitch of 0.5.


I have two older R lenses. The 28mm took a Series 7 filter plus retaining ring. I use an E48 filter in it's place. I also have an older 60 Macro Elmarit which used a Series 8 filter. I use an E60 filter on this lens.