I designed this staple to give better stability for adjacent items. As marbles roll there is a bit of wobble that can be introduced that might get a marble stuck.

These single staples will allow a marble to roll over the top.

You will need to print 2 of them for a single connection.

This is a snug fit that takes a little work. Using a needle nose pliers or the tip of a flat screw driver can help to apply pressure.

These staples are intended to be a snug friction fit, so you might have to adjust the tolerances slightly on your printer to achieve the correct effect.