I'm fixing a leak under my Pentair Nautilus FNS DE.  To access beneath the bottom half of the bubble I need to remove a hex nut (whose external dimensions are 3 1/8").  Because the nut is recessed in the bubble and workspace is limited, channel locks or a pipe wrench is not working.  I need a large 3 1/8" socket to remove.  Is anyone aware of where I can find a tool to remove this large hexnut.  Thanks in advance.  -Paul