Attached is the latest Mahle Clevite bulletin. According to them you should want the second ring gap to be larger than the top ring gap at operating temperature. They recommend 0.004" per inch of diameter. For a 4.375" ring the gap calculates to 0.018" or 0.46mm which I would round to 0.5mm. The top gap starts out bigger but the heat from the engine running causes it to close up the gap so it is smaller than the second ring gap.
