Well it appears to be a front brake disc - 260 x 12mm 5x112 PCD
Whether it's suitable for a 3.2 A3 is another matter. Audi code the front brake systems on the various A3s using what they call PR codes. The codes for the front brakes are codes 1LJ, 1LK, 1ZD to 1ZP. The code for a particular vehicle is shown on the Vehicle Indentification Sticker which can be found in the front of the Service Book or under the floor covering in the luggage compartment. On my particular A3 it's the code is 1LJ and is the 3rd item on the 8th row from the top of the sticker. This code gives the size of the brake disc required for each vehicle type.
Let me know the code and I will be able to tell you the size Audi specifiy.