Lensboard for Vivitar VI and 39mm lenses You'll need a retaining ring, and depending on the printing material, you might need to spray flat black paint once or twice to avoid translucency. Made in Tinkercad from a scan of an old lensboard

4-5 top and bottom layers in black PLA+ worked fine to avoid translucency

v2A is 2.4mm thick and has a small recess for a EL-Nikkor 50/2.8 as shown in picture, works very well. v5 added grip bars and works very well.