This is a filter attachment for cheap USB microscopes (variants with or without inbuilt screen). It is meant to clip in place of the transparent spacer that usually comes with those microscopes. The filter slides in and out and can be turned (so that it can be used e.g. to build an analyzer for polarized light microscopy).
Assembly: Cut out a 20-21mm square from filter material, place in slide, top with the square clip, add a drop of glue in each corner and let harden. Test the part that goes into the microscope for good fit (see below). If that works, glue all the parts together (choose orientation of the filter slide you like best, I think it looks smoother with the square cutout facing down).
The size of the clip depends on your printer/filament calibration, but I also found quite significant variations between different microscopes. For this reason I included several different diameter stls, and also a combined print with varying diameters (26.4 - 27.2mm). Also there is a choice between split and unsplit clips, probably split works better with somewhat flexy materials like PETG. For PLA I would choose the unsplit variant.

TLDR; If you just want to get going, "filter_assembly_withclips.stl" very probably includes everything you need except the filter foil.

Print Settings

Printer Brand:

Prusa

Printer:

No

Supports:

0.15

Infill:

Prusament PETG black

Category: Learning