I bought a rebuilt water pump and the square bolt on the side doesn't screw in very far, it feels like the threading is binding after I screw it in a tiny bit... What is this bolt for? And should it be easy to screw in our is it normal for it to be tight?

Thanks!

 

A photo might help.

 

Just uploaded one...

 

Looks like a pipe plug, not a bolt.

 

I don't know the name... Is this something that has to be adjusted to certain specifications?

 

It is a pipe plug. Normally that port is for a pipe fitting for a heater or bypass hose. The plug is for applications that don't use that port. The threads are tapered pipe threads, They bind so the plug seals. You'll want to use teflon sealer on those threads.