This is a different sort of Polymaker drybox hub.  It will work with any spool size, but it was designed to solve a problem with the smaller and/or thinner spools.  I ended up with some 250g TPU spools (oops) and on my other Polymaker HUB these small things would wander around, bang in to the sides and get tangled on the hub more often than not.  this locks them in place so they won't move (other than to spin around).

Like my other Poly Hub, this one also relies on a 608 ball bearing.  Any one will do, here is the one I used:
[https://www.amazon.com/dp/B073ST742Z](https://www.amazon.com/dp/B073ST742Z)

I suggest you print it out of PETG or better since it will sit in a drybox and if you make it out of PLA it will warp if you use the heater base.