The Argus C3 135-film rangefinder camera, made in Ann Arbor, Michigan from 1939-1966, is a bit of American history. About 2 million of "The Brick" were made, and many survive. The interesting thing is that the clunky camera used screw-thread-mount lenses that are simply adorable: tiny and exquisitely well made. Some lenses were made by Bausch & Lomb, others by Enna Werk in Germany, and a few came from Japan. Unfortunately, that doesn't make them great optics -- but they're OK, and did I mention that they're adorable?
Commercial adapters to modern mirrorless cameras are available, but a bit pricey. There is a little problem with inconsistent flange-to-film distances, so many adapters allow some adjustment.
Ok, so why 3D print this one? Well, first, it's really easy to print. Beyond that, I haven't seen any other C3-lens-to-Leica-M-body adapters. With such an adapter, these adorable little lenses can be used with the Techart Pro LM-EA7 adapter... which makes them able to focus somewhat closer and autofocus. Well, the LM-EA7 can only autofocus if you're within 4.5mm of focus movement from the correct focus, but that works very nicely using the LM-EA7 to tune manual focus: you use manual focus to shift the autofocus range.
The last four shots were taken using the LM-EA7 autofocus with the lenses shown -- and in the order in which they are shown in the first photo: 35mm, 50mm, and then two shots with the 100mm. All the sample images were shot wide open, and the images are not sharp to the corners, but they are sharp enough (and the lenses get sharper stopped down). Realistically, these lenses don't compete optically with modern lenses, but their old-timey character is nice in small doses....
MakerGear (any is ok) PLA
A very straightforward print. I often use "dishwasher safe" high-temp black PLA for this type of thing, but this was printed using ordinary black PLA. The screw thread feels very loose when you start, but it ends up sitting perfectly. The one down side is that I haven't yet tweaked he rotational position the lens stops at, so the lens ends up in a random rotational orientation... which is annoying, but harmless for C3 optics.
Note that the C3 thread prints directly and shouldn't need any post processing.
There is no post-print processing needed. However, there is a hollow spot on the side of the adapter for you to put a dot of paint to mark where the adapter inserts/removes from the M mount. If desired, you could also paint the raised "C3" name on the adapter to help make that stand out from other 3D-printed adapters in your bag.