Does anyone know what these are and what they are for?

[archiesdad (Stephen ward)]

I bought a yoyo from someone here,
He included a bag of strings, etc.
These are among the etc. If they are twisted, they light up and flash different colored lights. They are about 15mm in diameter and the same deep.
(upload://s1kJJKme2biS8X9A0OlKmNXCxxg.jpeg)

[hsb]

They are LED caps that attach to Lego-compatible hubs (many Rain City Skills yo-yos, One Drop Lego SEs.)

[rkalajian (Berv Throwington (He/They))]

You beat me to it

[Grendel (The Voice of All Grendel’s world wide.)]

Clearly a flux capacitor.

[archiesdad (Stephen ward)]

A fellow conspirator after my own heart.

[Captrogers (Brandon Rogers)]

I need to get me a pair I keep putting it off.