For use with the Bambu Lab P1 / X1 / X1C / X1CC Filament Spool Switcher & Winder by Miklos Kiszely and Inland Reusable Filament Spools. The empty spools aren't wide enough to be used with the Spool Switcher, so this spacer can be inserted between the two halves to make the spools compatible. The bolt holes are a little snug, but the bolts that come with the empty spools should still fit.