Lens was taken of from an old Zorki-4 but it'll couple with RF of any thread mount Leica or Leica clone. It also hides another (probably intended) feature. You can take off what looks like extension tube and RF coupler that looks like another tube inside extension tube (not in pictures I misplaced it) extension tube has a small locking screw and you'll end up with almost Industar-50-2 but in M39 mount.
Conversion to M42 is simple you need small ring with inner thread for M39 and outer thread in M42 it costs about 3 USD on ebay and then you'll be able to use it with M42 adapter to your preferred mount. Lens is of Tessar design but a bit sharper. It has some kind of coating, my Russian is rusty but there is lot of you that can provide accurate information about coating (correct translation) Lens was produced in two different finishes silver and a glossy black version.
This lens is by far smallest and lightest one that I know of and it looks totally ridiculous on any serious DSLR. It is advisable to use it with hood and if you cant find original one you can use film can from Kodak or any other brand and cut it so you end up with 30 millimeter tube and you can use container cap as lens cap on top of your new hood. Original hood is press on type and it'll hide f stop marker point.