I don't know if you are a troll or stupid, but you could just try a few wrenches, or Google. I'm guessing its 15mm though.
32mm
54mm
36mm.
12mm x 1.5 is the size you are looking for. This fits the Mazda 3, 6, 5, rx8.
36mm
32mm
Take a 12mm socket and try to fit it over one of the mounting bolts (the threaded part sticking out past the nut), if it fits you have 12mm idler arm, if not you have 14 mm idler arm
36 mm will fit the axle hub nut.
34mm or 36mm
I believe that is 18 mm.
12mm 12mm
22 mm