The filament spool maintainer FM-1 by 3dxtech has steel rods that filament is placed on. When using 3dxtech filament with plastic spools, the coefficient of friction is low enough that the spool will rotate. However, when cardboard spools of larger than 1kg are used; the spool tends to “jump” off the rails when the filament is pulled by the attached printer. This spool holder uses common 26mm bearings to make any spool compatible with the FM-1. You must print TWO of both models to support a single spool of filament. Eight ball bearings are needed per spool as well. By placing the adapters at any required distance, even HUGE spools of filament may be used. 

Ball bearings spec is:

26mm OD, 10mm bore, 8mm thick - 8x per spool to be mounted.

This 3d model is not created by 3dxtech.