This is a fairly simple spool holder for the large 300m spools with 3mm filament. The design is similar to many other holders, but this one was made using a CNC milled sandwich plate for the sides and M8 threaded rods to keep everything together.
If you don't have access to a CNC machine, the sides can also be printed in plastic or maybe lasercut in plywood or even acrylic.
Technical
I have used sandwich plate for the two sides, but as mentioned, other materials can be used (eg. wood or plexiglass) or ABS and PLA when printing the two sides.
The bearings are regular skateboard/roller blade bearings so they should be available everywhere for pretty cheap (used bearings will probably work OK too).