1/8 npt is usually a sender for oil pressure or an oil pressure switch (or a brake system part if it's not on the engine). Somewhere there is a component mounted with a 7/16 bolt that is into an oil galley...and it is NOT a head bolt since it isnt a grade 8.

Dont you have access to a shop manual that has a picture of the engine OR a picture of an installed engine? Should be able to look for a sender wire or tube.