This is a shim to adjust the alignment of your destination spool for the Pastamatic Spool Winder. The Pastamatic is an amazing design, but there are some of us that have had alignment problems with the winder mechanism. It would cause the spools to become extremely lopsided as shown in the first few pics. After adding a few shims, I was able to get much more even distribution of the winds (last pic). Each shim should move your spool about 2mm axially. It took 2 shims on the geared side for mine to be in the best alignment. I would suggest printing a few shims and it may take a few tries to fit your specific scenario.

Please share your experience below as I would love to hear any positive or critical feedback to help improve this.