This is a stackable glueless rack system for storing your filament spools and boxes. 

The assembly of the rack is pretty self-explanatory through the pictures. You connect a male part to a female part, do this two times to assemble a rectangle.

The diameter of the part is .725 and is designed to use low-cost and easily available 1/2 EMT conduit which has an OD of .706". Keep this in mind if you would like to source something else.

In my example, I bought 10ft pieces of EMT (for around $5.00) and cut them down to 2ft sections. You can use whatever length you want, but you may need to use the printed pieces in between long stretches of conduit.

These can be glued if needed/wanted, but the included dowel is a fairly nice friction fit, but that will depend on how well your printer is dialed in.