Heater hose connection in head. Brass plug fitment
 

Long story shortened. I have a NOS brass plug, for plugging heater hose connection outlet in 60HP display engine. I have 7 heads, 2 are cast iron. I have tried to fit the plug to each head. I can only get it to go into one head, which is cast iron. I have several NOS "iron" plugs, and cannot get any of those to work either, I have run a tap into the holes on the display engine, with no better results. I would sort of like to plug these holes for appearance sake. I know threads are correct in head and on plugs.

What am I doing wrong? Suggestions.

Re: Heater hose connection in head. Brass plug fitment
 

Not to insult you in the least, you are using pipe tap? Or is this not pipe thread?

Re: Heater hose connection in head. Brass plug fitment
 

It is NOT a pipe thread. Regardless, thread in head and on plug is the same. Just having trouble getting the plug started in the head.

Re: Heater hose connection in head. Brass plug fitment
 

What you're doing wrong is using the wrong plugs...5/8 UNF has 18 threads per inch, 3/8 National pipe thread has 18 TPI too. So, I'm assuming that the tap you are using is 5/8 UNF and your plugs are indeed pipe thread.

Re: Heater hose connection in head. Brass plug fitment
 

I believe Brian is right. Those holes in the head should be 3/8” pipe thread

Re: Heater hose connection in head. Brass plug fitment
 

Can't say on a V8-60 but on an 8ba they are definitely 3/8 pipe.

Re: Heater hose connection in head. Brass plug fitment
 

60 is pipe thread.