Lever locks

Lever

— the lock, the secret of which consists of a set of plates with curly slots (lever). The keys to such locks are colloquially sometimes called "horn" or "butterflies": on the working part of such a key there are two flat protrusions with curly cuts along the edges (however, there may be one protrusion). When opening the lock, the key deflects each lever at a certain angle, so that the slots in the levers form a “corridor” along which the bolt can move freely.

Locks with a similar mechanism are considered very reliable — in particular, it is almost impossible to open them with a master key.