Many small spools will not fit on the AMS Rotary Spool Holders; so I created a cap that clips into the end of the yellow posts (post numbers 2 and 4, with the hex shaped interface) that stops the spool from falling off. Fits spool ID as small as 34 mm.
I see someone made a design for posts 1 and 3 here AMS Lite universal small spool securing cap by Ludo - MakerWorld.
Let me know how theirs fits.