Tricopter 15.5mm Support Block

I'm currently building the Tricopter with Home Depot towel bar for arms. I was worried that the tubes could be crushed by tightening the bolts, so I made this spacer to fit inside the tubes and support them.

The opening is to allow wires to fit through on either side of the bolt. The lip helps keep wires from getting cut by the edge of the tube while folding the arms.