Abstract:
These are NES cartridge covers that will protect the contacts from dust and contaminants. They're fairly quick to print. I've only tested these on licensed cartridges so that means your mileage may vary for Tengen or other unlicensed cartridges.
Printing:
You may want to print with a finer detail for the ridges that will appear on the sides of the cover. These aid in gripping the cover for removal. The examples you see were printed on a Monoprice Select Mini v2 with AmazonBasics PLA.
The author hasn't provided the model origin yet.