I'd buy some new contact tips instead of ordering a special tap. Likely cost less. I am using some Lincoln Electric tips from Lowes, they have 1/4-28 threads.
Phil

I visited the best hardware store that I know of, about 15 minutes from my house. They have a large fastener selection. We were unable to find a compatible nut. The pitch is 24 threads per inch; that is what I measured, and they confirmed it. We tried metric sizes, as well as #12-24. Nothing fit. I measured the OD of the threads with a digital caliper, and came up with 0.230 inches, a little less than 1/4 inch. The manager of the fastener department said that it had to be a special thread, and I am inclined to agree with him. He said that anything 1/4-24 was probably pre world war II, but that the railroads still used it because they have some lights that were made that way.

I may order a special tap, size 1/4-24, knowing that it will be a little large. It may not work too well, but maybe better than the 1/4-20 that I tapped the hole for the first time. (For quarter inch, the standard threads are UNF 1/4-28, and UNC 1/4-20.)

Richard

That's exactly the approach and outcome I got - it looked line 1/4" 24 thread. It turned out tips were indeed metric. 6mm to be exact which requires #5 drill bit.

I'd buy some new contact tips instead of ordering a special tap. Likely cost less. I am using some Lincoln Electric tips from Lowes, they have 1/4-28 threads.
Phil

I agree on the new tips and the other thing to do is to hit them with some solder to make sure it's sealed.

Lincoln tips are 1/4-28. I've run Tweco tapered tips side by side with straight tips and couldn't tell any difference. If you want, chuck a straight tip in a drill and run it against a flap sander = a Tweco tapered tips.

2 questions, What size bell reducer are you using? It should be a 2-3/4 with the tips. and did you solder/braze the joint between the pipe and tip?

Jamison

Recently rebuilt my forge, it's small. Made it out of a 5 gal air tank. The inside chamber is roughly 4 in by 16 long, both ends open with hand brick cover for the back hole. Inside is 1in kaowool, then an 1 1/4 of soft firebrick cut into lags around the internal circumference. The bottom is a layer of hard brick for the floor. Then 1/4 layer of refractory cement.  It has two small burners from my old forge. Everything has cured the last week, today had first fire. The flame is an nice blue but the thing just doesn't heat up like the other one did. Could I not have the burners in far enough? 

Without a picture in the front of the forge so we can see the burner flame your question is like asking if the engine is big enough for the truck.

Asking if the burner is IN far enough shows you haven't read the Burners 101 sections of Iforge. Your description of how you built it, makes it clear you haven't read the Forges 101 section. 

Youtube how tos and all the various online videos are mostly posted by people who's only qualification is an internet connection.

Frosty The Lucky.

4 hours ago, bkon67 said:

today had first fire. The flame is an nice blue but the thing just doesn't heat up like the other one did. Could I not have the burners in far enough? 

Between your description of the flame, and the details about your forge's construction, I am inclined to view your 'problem' as more perceived than factual. In other words, you have built in a thermal battery layer, just like many old forge designs had a quarter century ago. As a consequence it will take additional time for it to heat up, so give it this time, and see if your main concerns remain, or just turn into general dissatisfaction about the details.

There was no intent to discourage, so get back to us with your findings, so we can discuss them with you. Did giving the forge more time to heat up do the rick?