This is a 120 cartridge which fits into a Polaroid pack film camera (Models 100 - 455) so it can use 120 film in 6x6 format. A back is also included which replaces the standard back.

The drive gear drops in place in the top right of the cartridge and should snap in with a slight click. The thumb gear installs with a thin screw through the hole in the cartridge. The film winds forward when the thumb gear is spun to the left.

Turn the door over so the bottom of the door is facing up. You'll notice 2 small notches at the left end between which the hinge is glued. Glue the hinge so the hinge loops are facing down, aligning it between the two notches.

Remove the original back door by removing the hinge (you may have to remove the plastic pieces at both ends of the hinge) and install the new door. It may be tricky to align the hinge, and it may need to be filed slightly to fit. It would be best to insert the hinge pin into the 3D printed door before installing it, to ensure the print left enough room for the hinge.

To load the film, install the 3 generic spool ends onto the 120 roll and take-up spool, and slip the take-up spool into the drive gear when the tab is aligned vertically (you may want to mark the gear when aligned vertically to later remove the spool). The loaded film spool sits in the left spool cutouts. String the film across and feed into the take-up spool, then install the pressure plate. Place the cartridge into the camera and carefully close the door, making the sure the retainer hooks engage.

You can either find a red filter to cover the film counter hole, and/or you can place a piece of black tape over it so light won't get in between photos. It's best to advance the film in the shade. You may also need to seal the light from the hinge using black tape on the outside or inside of the hinge.