A key for use in a cylinder lock with a rotatable key plug having a profiled key way, said key comprising:
- an elongated one piece key blade (120) with a relatively wide lower portion and a relatively narrow upper portion, there being a step-like transition region between the wider lower portion and the narrow upper portion,
- said one piece key blade (120) having a longitudinal profile groove (122) located adjacent to said step-like transition region and extending along at least a portion of the length of the one piece key blade, with an inner wall (124) surface of said groove being oriented substantially in parallel to or at a small angle, no more than 15°, to a an external side wall surface (123) of said lower portion of said one piece key blade,
- said longitudinal profile groove (122) having, at a lower part thereof, an undercut portion (129) adjacent to and inside a ridge portion (128) of the one piece key blade, the outside of said ridge portion forming a part of said external side wall surface (123) of said lower portion of the one piece key blade, in said relatively wide lower portion up to said step-like transition region (142), and the inside of said ridge portion facing being opposite said inner wall surface of said longitudinal profile groove,
- said longitudinal profile groove (122) defining, at an upper part thereof, a smallest opening width (w), as seen perpendicularly to said external side wall surface (123) of said lower portion of said one piece key blade, between an upper wall (144) surface and said ridge portion (128),
- wherein:
- said undercut portion of said longitudinal profile groove extends downwardly substantially in a vertical direction (VD) in parallel to said external side wall surface of said one piece key blade,
- said undercut portion (129) of said longitudinal profile groove (122), at its an innermost part inside said ridge portion (128), is extended or expanded downwardly, further substantially in a the same direction as said vertical direction which is substantially parallel to said side surface (123) of the key blade, (VD) into a longitudinal substantially uniformly wide pocket (135) having a uniform width with opposite inner and outer substantially parallel lateral wall surface portions (132, 133) and wherein said inner wall surface of said longitudinal profile groove adjoins the inner lateral wall surface portion of said pocket, and said inner lateral wall surface portion of said pocket extends downwardly to a lowermost transverse end wall (134) surface, which is substantially flat or slightly curved, and which is substantially parallel to a lower edge portion (127) of the lowermost edge wall surface of the one piece key blade and which faces upwardly in a direction being parallel to central plane (A) of the key blade opposite to said vertical direction (VD) towards said upper wall (144) surface of said longitudinal profile groove (122) with said opposite lateral wall surface portions (132, 133) of said pocket (135) being substantially parallel to said external side wall surface (123) of the flat one piece key blade (120).