That's the bolt that holds the oil pump in place. There is a round notch in the oil pump housing that when the bolt is screwed in, that tapered end of the bolt screws into that notch. You may have to wiggle the pump around to get the bolt to go into the notch. Then it is just snugged up (not tight) then torque the nut to hold the bolt in place. Also you may have to turn the crank to get the bolt started.
