A key plug for a cylinder lock, comprising:
- a cylindrical body with a cylindrical contour around a rotary axis (C), configured to enable a rotary motion of the key plug in a cylindrical bore in a housing of an associated cylinder lock,
- a longitudinal keyway extending in the cylindrical body along a vertical mid-plane (MP) passing through or adjacent to the rotary axis (C) and being configured to accommodate a substantially flat key blade of an associated key for releasing the cylinder lock,
- a row of radially oriented central bores being located in a vertical central plane (VP) passing through the rotary axis (C) and communicating with the longitudinal keyway,
- a row of central locking pins being movable in the central bores and being configured for locking the key plug against rotation relative to said housing unless the key blade of said associated key is inserted into a longitudinal position in said keyway which enables a release of the cylinder lock by turning the key and the key plug in said cylindrical bore of the housing,
- wherein a cross-sectional profile of said keyway, along a major longitudinal portion of the key plug, is confined within a rectangle having a height being at least 2.5 times greater than a width thereof, said cross-sectional profile including:
- a lower relatively wide part, having a maximum width being substantially the same as or slightly less than the width of said rectangle, the maximum width being 75% to 100% of the width of the rectangle, measured between a first lower side wall and a second lower side wall, and
- an upper relatively narrow part serving to enable an interaction between an inserted key blade and said movable central locking pins in said central bores, and
- possibly an interconnecting part, adjoining to said lower and upper parts of the keyway so as to extend therebetween along said vertical mid-plane (MP), and
- wherein:
- said upper relatively narrow part of the keyway has a relatively small lateral width being no more than 33% of said maximum width of the lower relatively wide part of the keyway and extends obliquely upwards along a first direction (P1) pointing away from said second lower side wall of the lower part and being inclined at a relatively small angle α, in the interval 3° to 12°, relative to said vertical mid-plane (MP), and
- the sideways or lateral location, within said rectangle, of said upper relatively narrow part of said keyway, including first and second upper side walls thereof, is such that an imaginary downward extension thereof, substantially in a second direction (P2) opposite to said first direction (P1) down to said outer cylindrical contour of the key plug, will fall onto said outer cylindrical contour at a same second side of said vertical mid-plane (MP) and inside said second lower side wall of the keyway.