Not sure what it is yet, if nobody answers it by tomorrow morning I'll glance at my car tomorrow. As far as the hex socket, they make 5.5mm.

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k