Each Lubitel camera has its own charm! For this project it translates to the need of matching a lens rim to the camera body. From my experience, it can be done just by measuring the body (the diameter of the inner screw thread). Essentially, you need to print and match until the proper rim size is found. To simplify the process, I prepared a set of STL files with rims of different sizes. The files are named according to the following convention:

• the first number marks the outer screw thread clearance: the higher the value, the looser the rim-to-body engagement. I suggest starting with the clearance of 25 (0.25mm), then print the rim and test it against your camera body. If the engagement is too loose,  switch to a lower clearance value (i.e., 20 == 0.20mm) and repeat printing. If the engagement is too tight, then switch to a higher clearance value (i.e. 30 = 0.30mm) and repeat printing. The best result is when the rim turns smoothly without applying excessive force.
• the second number marks the inner screw thread tightness: the higher the value, the tighter the rim-to-lens engagement. The default value of 10 (0.10mm) worked well for of the lenses I worked on. The main thing to avoid here is a loose engagement, because it results in the lens not being coaxial with the rim. Please report your case if 0.10mm tightness doesn't work for your lens.
• All the models in the STL files bear the same marking (clearance x tightness) on the inner surface of each rim - it should help not to confuse the prints.

The lens rim 3D model is designed for the following printing settings:

• 0.45mm nozzle
• 0.20mm layer height
• PETG filament
• single perimeter
• 3 top/bottom layers
• 5-10% infill

Please, before printing, pay special attention to first layer calibration. "Elephant foot" would ruin the printed lens rim for sure because the rim's teeth would not mesh properly with a Lubitel's lens rim.