This a little special purpose design to try to solve a problem for A Dragon In A Pie Costume. She's converting to a Diamond hotend that mixes three filaments at the nozzle. Since the BigBox has just two spool holders, this presents a problem. I tossed together this design to let her use the basic BigBox layout by mounting two small spools on either the right or left spool holder. The tandem bracket threads onto the existing rods. It requires two M4x35 socket cap or button head screws and eight 634ZZ bearings. The outer spool will not be clamped so some testing for stability will be required. This will only work with narrow spools although one could use longer rods if required but be careful not to put too much of a load on it if you do.