The TTArtisan 28mm f5.6 lens is a modern remake of the classic Leica Summaron 28mm f5.6 lens from the mid-50s- a lens which Leica is also currently remaking (though at a substantially different price point). The design (including the infinity lock) is very thread-mount, but this is an M mount lens, so it'll fit directly on any M mount camera or adapter. Build quality is pretty good, with an all-metal body and smooth focusing. Clean glass, good function. Also, it's gold coloured. Includes front and rear caps (hilariously stuffed with weights to make them feel more substantial) and original box.