Male plug to fit unknown female drain thread.

I am refurbishing a stainless steel open top tank to melt wax for beehives. The tank has a threaded section of welded pipe with a female thread for a drain in the floor of the tank. The male plug is missing and I'd like to get one. The inside diameter appears to be 1.5 inch across with relatively fine thread. I've looked up charts and this could be a 1.9 inch OD, 1.5 inch ID 11.5 TPI thread. But I am not sure. Is there a more definitive way to determine this? Also, I am unclear if this is tapered or straight. I assume this would make a big difference? Since the tank will be heated to approx 300F, is there a particular metal (galvanized, brass, etc.) I should be using? I assume I can use teflon tape to ensure a good seal. Any thought/comments greatly appreciated. Many thanks.

A little more information.... Made more precise measurements and it is likely 1.5 inch ID, 1.9 inch OD 11.5 tpi female thread. There are only 8 threads so difficult to tell if it is tapered or straight. It appears to be stainless. My research tells me tapered is more common so I will try getting a tapered male plug. If however, I am wrong and I insert a tapered threaded plug into a straight thread female, could I damage the female thread? Should I get one of each (Male/female) plugs to be on the safe side? Thanks..

Use plastic fittings for thread testing so you don’t damage the tank

Any chance you can post a picture?

With only 8 threads it doesn't leave much to measure a taper, however, the taper would be 1/16" (0.0625") per 1" in length, so it would seem to me that if you got something with a diameter that would barely fit into the hole, you would be able to tell if it had a taper.

Also, remember that a tapered thread is tapered to form a tight (leaktight joint) while a straight thread just provides the torque on a seating surface that typically would have some type of washer for the actual seal.
Not sure what you're looking at has any hint to this.

Thank you all for reply. Greatly appreciate the advice. I bought a stainless steel MNPT 1.25 plug and I get 4-5 turns before it starts to snug up. So it seems it will work. Due to 300 degree F, any thought regarding Teflon tape vs. liquid pipe dope? Again, many thanks. Pete

inexpensive sealant that is rated above 300 degrees

https://www.permatex.com/products/t...nts/permatex-high-temperature-thread-sealant/

Teflon tape is a good ideal seal , the temperature rating of Teflon tape is - 100 degree to 260 degree.

Thank you!

you might think about putting a right angle ball valve on the tank. From one beekeeper to another. Tough to drain hot wax with just a plug.

Great idea Wood4d. Thanks. Had given that some thought but not sure which valves would be rated for the heat (approx 300F). Would require a few elbow and extensions to bring it out from from under the tank. Would have to be threaded, not soldered.

Sounds like you dip your hives as well. May I ask what you use for a burner system? My tank sits in an angle iron frame with 6 inch steel casters underneath. With the caster attachment plate, height from the ground approx. 7 inches. I've thought about either making or buying pipe/tube burners vs. round burners. I can Mig/Tig weld as needed. I'd need 2-3 of them. For example, Home Depot has inexpensive adjustable length tube burners with adjustable venturis. I'd use a long (15') propane hose attached to a low pressure adjustable control regulator on a 20lb tank. Length is for safety purposes so I could shut it off in case of trouble (as in 650 lbs of wax catching fire) and keep propane tank at a safe distance. I'd rather have one valve a distance from the wax tank instead of separate valves at the wax tank for each burner, but I'm not sure I'd get good adjusting ability without those. So burners are easy, propane tank with the adjustable regulator valve is easy. The tricky part will be figuring out how to make up a manifold that interfaces with the burners with appropriate orifice sizes in the venturis. I am scouring the internet for ideas. Seems folks use 1/8 brass threaded pipe with appropriate tees and elbows and end caps. They then custom drill the end caps with orifice holes that interface with the venturis on the burners. It will take some trial and error I suppose. I need to do it safely but have already spent a small fortune on tank, wax, setup. Wife is ready to shoot me. Thank goodness for trigger locks. Want to keep additional costs down. Need to get this done in four weeks to make splits before the hives decide to swarm. Thanks again for your thoughts.

The valves have wog rating on them. 600 would be good. its pretty much standard for a decent valve. think about an old 60k furnace burner or better yet a small boiler. the boiler setup is better because its always horizontal. in my experience the gas valve and burners are not usually why heaters get scrapped. I used to have a pile of them until wife said no to piles of scrap stuff. you could make a better bracket than you get with the equipment if you can weld. Most equipment has propane conversion kits available. If you like the pipe idea every stove {just about} has a propane conversion kit taped on the back. You get orifices corresponding to the burner size. I have electric stainless tanks with the wax heated in water baths. They have single water heater elements mounted so they are 110 volts. I got them from a commercial beek who just sells his wax now. You dont need stainless unless you want it foodsafe. In your case I would go with galvanized pipe because its cheap and I would increase the size to 3/4 . Lowes has a great ball valve handle hose bib you could mount on a steel plate. My wife is a beek too, so $ isnt an issue unless im wasting it, which does happen sometimes. good luck

Thanks again wood4d. If I am understanding you, 3/4 pipe for drain with 600 wog rating for tank drain valve. I see that they are rated for 300 degrees. I plan on heating up to 275 so will be close. I'll see if I can find higher temp rated valves. As far as the gas burner setup, yes, I considered using 3/4 black or galvanized pipe as a manifold and also as burners (with slits/holes for flame). If I do this, i'll need to make a venturi set-up and trial and error custom drill orifice holes to get the flame right. There are a few youtube vids where this is done. Was just thinking the Home Depot tube burners with venturis vents would save me some labor. At $16 each, not a bad deal. Just have to reduce from 3/4 to a size that fits into the venturi tubes with a cap on the end that I can drill out to make appropriate sized orifice ports.
As far as bees go, I'm in NH so still well below freezing at night. No pollen yet but at least they can make their cleansing flight.

Thanks again!