I had a lot of trouble getting the locking shim that Bambu provided for their spools to print in PETG Basic, so I re-created it in Fusion, made a few little edits (very tiny adjustments in thickness and a larger more stable base), and exported as a STEP instead of an STL. The provided profile is not fast, but it works very cleanly with BBL PETG Basic and other more advanced materials - made some in ASA as well.

Reddit pointed out that there's not really a great tutorial out there on how to use these. Et voilà!

Your spool will have four slots. Two small, two large. Find either of the large slots and insert the shim straight in to it.