This is a press fit anti reflection device (ARD) or killflash for scopes with a 34mm main tube. There are 2 models available, one with a full hex grid that will provide a wider angle of reduced reflection and one with a center cutout of the grid that may help at 1x to reduce any impairment of vision through the optic.

These will function just fine printed in whatever your filament of choice is, however if youre planning to be out in the sun with it frequently something like an ASA, ABS or Nylon would probably work best.