EDIT: I have made a newer version of this at https://www.thingiverse.com/thing:3233044
Saw some spool holders but wanted to try to create one of my own for practice. I took inspiration from https://www.thingiverse.com/thing:2965069 by mamejay. This uses one bearing per holder. 2 are required to hold the spool. The smaller hole is sized to fit the threaded rod that comes with the Anet A6 spool holder. You can put a 35mm od bearing in the larger hole.
i printed it with the smaller end down so I wouldn't need supports in the bearing hole. I needed to use a raft because it came off the bed when I was just using a brim.