A spool that uses universal mesurments to be able to use refils, print the 2 sides and then the 3 middle parts, screw in the first 3 parts with one side then place the refill inside then add the second spool part and screw in 3 more screws, usualy refils have plastic clips that you have to take out, take them out and its just like the normal spools that manufacturers give, as said its reuseable 

until now ive only tested sunlu filamet but the mesurments are universal any refill will work