So far, the smallest penis has been Minicage, but that's no longer true. The smallest chastity cage of the world is now Microcage.

The cage consists only of a thicker metal ring and a flat metal cap with holes for urination. It reliably prevents the slightest hint of an erection.

It can also fit a penis, which is about 7-8 cm at rest, but its use is more for experienced users. In a completely calm state, the penis needs to be pushed a little to manage to connect the key to the ring and lock it. But it's not painful or uncomfortable.