  We recognise the appearance of a Focus Point (FP) in the transverse momentum
distribution of either leptons originating from a BSM $Z^\prime$-boson decay,
after a simple normalisation procedure. Exploring the properties of the FP we
will be able to define in a general way a new observable, the Focus Point
Asymmetry ($A_{\rm FP}$), which can be used to set constrains on the $Z^\prime$
width. We discuss the potential and the sensitivity of the $A_{\rm FP}$ in as
diagnostic tool for $Z^\prime$ physics, considering various $Z^\prime$
phenomenological realisations.
