I couldn't find short threaded rods, so I had to make my own. I used carriage bolts because it would be easy to cut the heads off and have them all be generally the same length. I cut them with a metal-cutting bit on my Dremel.

This step was hard to get right and I had go back on each one and sand off extra bits which were making them difficult to screw in.

Suggestion: buy pre-made short threaded rods.