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.