The sight plug is a 5/16 x 3/16 20TPI plug. It is hollow along the threaded shaft.
I don't have the *exact* measurement of the hole, but middle of the raised fuel bowl boss is a good starting point... basically anything that will put the lower 13rd of the plug under the float while the float has the fuel input closed will work. Its just to see if there is fuel in the bowl (as per the 4/43 TM9-801.
