I'm trying to find the correct size thread chaser to use on the water inlet on my carbide generator. The tank is NOS and the brass cap is really difficult to get started and I don't want to cross thread it. I would like to clean the threads with a thread chaser but not sure what size to use.
For finding thread form and size, invest in some thread gages, you'll want USS thread, coarse and fine, they look like this:
Then purchase the matching thread file to chase the threads back to form. They look like this:
If you don't buy the tools you need, you will eventually pay for it, but not have your tool. Henry Ford
With a tap you stand a really good chance of tearing out the threads. Using a thread gage and a file is your best approach. Have you looked at the first thread very carefully, both male and female, sometimes it's rolled over and straightening it out is what's needed .
Is there a chance he's looking at straight pipe threads?