This is a Slim Spool Locking Shim. It is designed to make sure the two halves of your filament spool do not become separated, which is a filament disaster.

This is a fast print - it only takes about 15 minutes. The locking shims use less than 1 g of filament each. The print profile includes two shims. 

This model is designed to work with spools that are similar to and compatible with the official Bambu spool. This model is based upon the Bambu Spool Spacing Shim. This version is different in that it is slightly smaller laterally, so that it fits a little easier into tight gaps. It is also quiet a bit shorter. The Bambu shim is 18 mm tall, and this one is 12 mm tall. 

The 18 mm Bambu shim wouldn't fit in my Small Sample Filament Spool because the two halves of the small spool are too close together. I modified the Bambu shim to make it fit.

It was designed specifically for my Small Sample Filament Spool. But it should work with any spools that attach the same way the Bambu spool does. It should be especially good for small spools. 

Public Service Announcement: If you buy Bambu filament refills, or use any refills with Bambu compatible spools, you really should use a locking shim every time you install a refill. They are a fast print, and cheap. They will make sure the two halves of your spool stay locked. If they come unlocked, you could lose containment and turn a nice new spool of filament into a tangled mess. Just do it.

If you look at the center hub of your Bambu-compatible spool, you will see large gaps and small gaps. These shims fit into the large gaps.