What is this?

I picked up this bike as a fixer upper. Good thing I looked over the entire bike since it was missing this part.
Does anyone know what this part is called? I'm guessing it is more than just a pin. If you have a link where I can buy the part would help also.
TIA

That hole in the axle bolt is for putting a rod or screw driver in to keep it from spinning while you tighten and torque the bolt. Nothing goes in it after that has been done. I usually hand tighten the nut side first then torque the pinch clamp first before fully tightening/torqueing the bolt so that hole is not needed. Torque specs and setup is in the manual.

As said, nothing goes in that hole, for pulling axle or holding it.