This is a Brembo PS 15 Master Brake Cylinder for the front of the Ducati Bevel 750 and 900 SS, Pantah 600 650 750 and Guzzi model like the V7 850 T Lemans, This is the later type with transparant fluid reservoir. The piston moves freely but I should replace the seals as a matter of safety. 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