No hardware or glue is required—just a standard rubber band (preferably with a larger diameter; I used one from JD.com that’s about 7 cm long when folded and claims to stretch up to 40 cm). Installation is straightforward; refer to the images:

1. When assembling the base, first put the three side rails together, then attach them all at once to the bottom plate.

2. Secure the top section by mounting two pulleys at either end of the bearing.

3. If you don’t have a multi-color system, you can substitute paper or fabric red flags and affix them to the rubber band using double-sided tape.