There's a Zheng3 Kickstarter in the works, so the printers have been furiously extruding protoypes since Christmas; sharp-eyed readers will note that zheng3.com has been largely silent since Santa shimmied down the chimney. We're going through filament like poop through a goose over here.
Ever on a shoestring, we try to keep costs down as much as possible, which means going hither and yon to find filament. At this stage in the hobbyist 3d printing game it's premature to ask for some spool standardization up in this humpty-bump, so we've a stack of myriad spools, no two diameters alike.
This spool spindle is designed to fit a 52mm spool.
This three-part solution (thirteen parts, if one counts the 4.5mm BB's) is designed to use a Tinkertoy rod as an axle and is a much, much smoother ride for your filament spools.
I found inserting BB's into the original 608 bearing to be frustrating so I split the bearing in two and left it to the end user to super glue the parts together.
The walls of the inner spool are by necessity quite thin; I recommend multiple shells or high infill for that part.