I assisted the rear brake change on my Avensis, and my mates at the garage has the tool with left and right handed tools. You will know which is the correct way, because after winding back the right piston, the other mechanic used the same tool on the left-hand piston/calliper. Due to the thread being the wrong way, it would not budge. I suggested getting the left-hand tool, and the piston wound back in. It is a bit stiff but the piston goes in. Basically you cannot use the wrong tool on the wro