This is a chrome plated control plate for Jaguars and similar guitars. This plate typically houses two black wheels which control the volume and tone of the 'rhythm circuit', and a slide switch that turns the rhythm circuit on and off.
Dimensions -
Maximum length: 133mm
Maximum width: 61mm
Right to middle mounting hole distance: 55.5mm
Middle to left mounting hole distance: 89.5mm
Left to right mounting hole distance: 111.6mm