Master lock, that is, in a group of master locks, the master lock key can open any master lock, and the master lock key can only open its own corresponding lock, and the keys between the master locks cannot be opened each other, nor can the master locks be opened.

The master lock and the slave lock comprise a lock body and a lock core, and the lock core and the lock body are respectively provided with a plurality of bead holes which are communicated with each other; A lower bead is respectively arranged in the bead hole of each lock core, and the lower bead is a cylinder with different lengths; A middle bead and an upper bead are respectively arranged in the bead holes of each lock body, the middle bead is a cylinder with different lengths, the upper bead is a hollow bead, and a spring is arranged in the hollow; The ends of the lower bead and the middle bead are opposite; The master-slave lock also includes keys with different key tooth depths. When the key lifts the lower bead, the two opposite ends of the lower bead and the middle bead are on a straight line, which is aligned on the interface between the lock body and the lock core.

I don't know if it originated in China, but many manufacturers still make locks and have this patent.