We all make mistakes. This part will easily fit through the 1.5" hole and allow the .75" Drain Assembly or Shut Off Valves to screw into it.
If you are going to install the bulkhead fitting inside of a typical 55 gallon barrel with the 2 spin in top plugs - this is 'how to':
Unscrew the lock nut from the shaft of the bulkhead fitting.
Remove one of the plugs in the top of the barrel
Using a long piece of wire - put a slight bend in it near the bottom 6"-> run the wire through the bulkhead fitting (so the shaft is pointing down toward the tank)-> through the plugs hole->and down and out of the hole that you want the bulkhead head fitting to come out through.
Let go of the bulkhead fitting and let it slide down the wire to the opening
Pull the bulkhead fitting through and screw on the lock nut until snug - over tightening may cause a leak