I designed this originally for the A1 External spool holder. I liked how it worked and its simplicity so much that I made a base piece to use the same setup on my Ender 3 V2.  It slides on the original spool holder bracket. I like this design because it doesn't take very long to print it compared to other designs. 

The original upload for the A1 is here → https://makerworld.com/en/models/178102#profileId-195998

The hardware required for this build is:

(4) - 608 ZZ bearings which are very common. I got mine from my wife's old roller blades.

(2) - Screws, 50mm long x 3mm shaft and 4.8mm outer thread diameter, but most importantly a tapered head larger than 8mm so it aligns and holds the bearing in place.

Installation:
-Take one 50mm screw, place a bearing on the screw and make sure the head of the screw will not pull through the bearing.

-Next place the bushing on the screw and then another bearing and lastly the washer with the flat side facing away from the bearings.

-Screw all of this into the Main Center piece and then slide on the Spool Main part and that's it.

-Repeat the steps for the other side if you want it to hold two spools.