The half circles with the nubs.. What were they made for?
Wait, you mean the ones that are red rod length?
Oh, Those are for the track, too. The tips of them is what you put the tubing on. Their not any different then the yellow connectors. They just have a tip that you can stick tubing on.
They were made for the original k'nex coaster. It's a red rod wide so to keep the track from squeezing together, they made the nubs.
i thought they were orange
the orange tubing slides on to them as far as i know.