A key element having a flat key with a key head and a key shank which extends along a key axis from the key head to a front key tip and has two parallel flat sides and two mutually opposing narrow sides. On at least one of the flat sides, an inlet groove extending from the key tip in parallel with the key axis is provided which has a non-constant depth along its axial extent. The inlet groove can have a first depth, in particular in an entry region, and a second, greater depth in a coding region remote from the key tip. The inlet groove is undercut, as a result of which an expanded sensing head of a block tumbler can engage therein.

A key element having a flat key with a key head and a key shank which extends along a key axis from the key head to a front key tip and has two parallel flat sides and two mutually opposing narrow sides. On at least one of the flat sides, an inlet groove extending from the key tip in parallel with the key axis is provided which has a non-constant depth along its axial extent. The inlet groove can have a first depth, in particular in an entry region, and a second, greater depth in a coding region remote from the key tip. The inlet groove is undercut, as a result of which an expanded sensing head of a block tumbler can engage therein.