FLAT KEY FOR A CYLINDER LOCK

A flat key (1) for a locking cylinder (101) has substantially flat and approximately parallel flat key sides (2', 3'), a key rear section (4), and a key front section (5) opposite thereto. The key front section (5) has a toothing that is used to position tumbler pins which are divided into core pins (112) and housing pins (111) and which are spring-loaded against the key front section (5) in the direction of the key rear section (4) and into corresponding bores. Grooves (11', 12', 13', 14', 20'-25') in the form of profiled variation elements and profiled guiding elements are provided in the flat sides (2', 3') of the flat key (1), wherein at least two grooves (11', 12) of one flat side (3') of the flat key (1), which are preferably part of the profiled guide, overlap and are undercut in opposite directions. According to the invention, a depression (15', 16') is provided in the outer flank (11a', 12a') of at least one of the two grooves (11', 12'), preferably both grooves (11', 12'), at least one region (15b, 16b) of said depression not being visible from the side. The two depressions (15', 16') are preferably symmetrical so that the depressions can be produced using a T-slot milling cutter (60). Such flat keys (1) cannot be completely measured from the side even when using a laser scanner but can still be produced solely by milling.