Reversible flat-bladed key for insertion into a key channel of a cylinder lock with Y-Z faces of the key blade parallel to side-surfaces of the key channel, the lock having a row of mutually similarly shaped rotor pins each having substantially coaxial tip and body, and each being located at a predetermined axial Z-coding pin location along one of the side-faces of the key channel, and each being displaceable along a coding axis of the key, wherein the coding axis is inclined at a coding angle (α) to the said X-Y face when the key blade is inserted in the key channel; the key blade having a thickness axis X, a transverse axis Y and a longitudinal axis Z, the X, Y and Z axes being mutually orthogonal and the Y-Z surfaces being substantially parallel to the Y-Z plane containing the Y and Z axes; the blade comprising at least a first row of a plurality of first coding recesses each formed at a predetermined Z-coding recess location (Z 0, Z 1, Z 2, Z 3), along the Y-Z surface of the blade, corresponding to one of the Z-coding pin locations; each coding recess having one of a first plurality of predetermined mutually different first coding recess geometries (2 1, 2 2, 2 3), each coding recess geometry comprising a pin contact surface region, referred to hereinafter as the contact region, for coded contact engagement with a corresponding one of the pins of the cylinder lock, wherein each coding recess geometry is formable by an end mill type cutter having a first rotation axis orthogonal to the plane of the blade, or by a side-and-face mill type cutter having a second rotation axis (R') parallel to the plane of the blade, and wherein the contact regions of the different coding geometries are located at different predetermined C-locations along a C-direction (C') parallel to the coding axis; characterised in that the coding angle (α) is between 30° and 60°, each of the coding recess geometries (2 1, 2 2, 2 3) has a transverse cross-section profile comprising a first flank containing the contact surface region, such that the contact region is inclined at a second angle (γ) of between 30° and 60°, to the blade plane, and substantially orthogonal to the coding axis, and a second flank, on an opposite side of the recess across a width of the recess from the first flank, and wherein the said coding recess geometries (2 1, 2 2, 2 3) differ in width along a transverse direction, parallel to the Y axis, and in depth along an X direction, parallel to the X axis, such that the first flank of each coding recess shape is at a different transverse location, and such that the second flanks of the coding recess geometries of all the said plurality of coding recesses are substantially mutually co-aligned in a plane containing a longitudinal axis (Z A) parallel to the Z axis. the key blade having a thickness axis X, a transverse axis Y and a longitudinal axis Z, the X, Y and Z axes being mutually orthogonal and the Y-Z surfaces being substantially parallel to the Y-Z plane containing the Y and Z axes; the blade comprising at least a first row of a plurality of first coding recesses each formed at a predetermined Z-coding recess location (Z 0, Z 1, Z 2, Z 3), along the Y-Z surface of the blade, corresponding to one of the Z-coding pin locations; each coding recess having one of a first plurality of predetermined mutually different first coding recess geometries (2 1, 2 2, 2 3), each coding recess geometry comprising a pin contact surface region, referred to hereinafter as the contact region, for coded contact engagement with a corresponding one of the pins of the cylinder lock, wherein each coding recess geometry is formable by an end mill type cutter having a first rotation axis orthogonal to the plane of the blade, or by a side-and-face mill type cutter having a second rotation axis (R') parallel to the plane of the blade, and wherein the contact regions of the different coding geometries are located at different predetermined C-locations along a C-direction (C') parallel to the coding axis; characterised in that the coding angle (α) is between 30° and 60°, each of the coding recess geometries (2 1, 2 2, 2 3) has a transverse cross-section profile comprising a first flank containing the contact surface region, such that the contact region is inclined at a second angle (γ) of between 30° and 60°, to the blade plane, and substantially orthogonal to the coding axis, and a second flank, on an opposite side of the recess across a width of the recess from the first flank, and wherein the said coding recess geometries (2 1, 2 2, 2 3) differ in width along a transverse direction, parallel to the Y axis, and in depth along an X direction, parallel to the X axis, such that the first flank of each coding recess shape is at a different transverse location, and such that the second flanks of the coding recess geometries of all the said plurality of coding recesses are substantially mutually co-aligned in a plane containing a longitudinal axis (Z A) parallel to the Z axis.