Bolt threads

[Jerryh3]

Is there a NPT equivalent for a .500-13 UNC? Trying to rig up something for the Mercruiser drain plugs and need to do some shopping.

 

[etracer68]

Re: Bolt threads

To answer your question, NO. A 1/2-13 is 13 threads per inch, the closest diameter would be a 1/4-18 NPT, and the missmatch on the threads per inch would be to much, besides a pipe thread is tapered. A 1/2-20 would be closer on threads per inch. Either way it should be drilled and tapped, and that may put chips in the LU. What are you trying to do?

 

[Jerryh3]

Re: Bolt threads

Replace the blue drain plugs with a thread to barb connector for a central drain/flushing setup.

 

[NetDoc]

Re: Bolt threads

What you want is a banjo bolt & fitting.

Fitting


Banjo Bolt​

 

[bruceb58]

Re: Bolt threads

Whatever you rig up is going to get blocked with crud so you need to remove it anyway. I would stick with the standard plugs.