Standard single peg with 6mm axle. K'nex hub compatible. All pieces associated with the marble run are designed to be mounted with these pegs.
There are holes for thumbtacks and an indent for 1/2" magnets to use for chalkboard demonstrations. Eventually, this will be developed into a modular blackboard physics 'thing.'
Designed in OpenSCAD
Set of 20 takes 3 hours and 23 minutes on default settings with our flashforge.