Fitting for a window or door

A fitting for a window or a door for operating a closing mechanism, comprising handle means including at least one handle (10) having a handle neck (12), the handle neck being axially tight but pivotally supported on or in an installation body (20), which body is adapted to be fastened to a flat support, in particular to a room closing element, and further comprising a polygonal bar (30) engaging into or penetrating the installation body (20), the bar (20) being connected for rotation with the handle (10) for actuating the closing mechanism, wherein a coupling assembly (K) is provided between the handle (10) and the polygonal bar (30) such that a torque transmission is achievable from the handle (10) and the polygonal bar (30) but is blocked from the polygonal bar (30) to the handle (10), the coupling assembly (K) having two drivers (15,35) arranged between the handle (10) and the polygonal bar (30), which drivers are adapted to be coupled together in a positive or non-positive manner and either directly or via at least one coupling member (36,40,42) under a predefined clearance of motion (B) between neighboring driver surfaces (17,37) in such a way that a torque acting on the handle (10) will be transmitted to the polygonal bar (30), but that a torque acting on the polygonal bar (30) will stop its movement and will block an actuation of the closing mechanism.