I was printing the Filament Bracket by waleriusDesign  and I didn't want to go buy dowels because I'm cheap and I have a 3d printer - and I know I'm not the only one!  Hopefully this can be helpful!

The included plate is composed of 3 mid sections, 1 male, and 1 female end.  This totals 710mm (just under 28 inches).  You can print as many mid sections as you need 225 mm/ ~9 inches each.  

Designed to be printed with NO supports.  Flat on the bottom to make this possible.  Its not the fastest print, but you could speed it up by using 2 walls instead of 3 at the cost of strength.  
 

Designed for the above print at 24mm, but could easily be scaled up or down to be any size you need.  Maybe. 

Happy Printing!