All these work the same: They are not screwed on, but can be bent open (slightly) and snapped on the lens. Locking the adapters is done by screwing a GuerillaBeam (or a compatible nut) on them.

This is much more robust than printed mechanical copies of the original mechanics.

These adapters are part of the GuerillaBeam, the worlds first 3d printed (portable) slide projector system. Please check it out, I even made a translation for it! :)

Printing tips:

Print with the screw thread facing upwards. 1mm shell and 23% fill are usually enough. Layer heights up to 0.3mm are possible, recommended value: 0.2mm. Printed successfully on an Ultimaker with PLA.

Regarding M42:

There are two versions for M42: One for older lenses (mostly before 1985) which exhibit larger undercuts with ~1.5mm height, and one for more recent lenses with smaller undercuts (~1.2mm).