This is an Aprilia Head Light for a Ducati Bevel Single 175 200 250 350 and 450 and other Italian motorcycles of the period like Moto Guzzi Benelli Aermacchi etc.  The window is 150 mm.  It has some internal wiring and a switch on top of the bucket and also a removable Fiat key. Nice used state, see pictures. 

Ducati roundcase, Imola, Greenframe, SS, SD, GTS, MHR, SSD, Darmah, squarecase, S2, sport, supersport, Borrani, Ceriani, Scarab, Lockheed, Marzocchi, Brembo, monza , diana, mach, mach1, dm250, dm350, dm160, 160, 450, dm450, desmo, desmodromica, elite, elite 200, brembo, 900SD, Mark 3 , mark 2, CEV, 750, 750GT, 860GT, 900GT, MV Agusta 750 America GT SS