Very wise advice, heat helps but it must be controlled and as you need to lubricate the threads I’d suggest boiling in sump oil, base oil boils at around 500 Fahrenheit but some high grade motor oils will reach 1000 degrees. Brazing will melt at about 800 Fahrenheit so the average sump oil should br OK.
An easy check is to get a piece of water pipe, fit two end caps and drill a small hole in one, say 1/16”, put some water in it, stand in the oil and when steam comes out the temperature of the oil is around 212 F. which should be hot enough.
Then before it cools use an “Easy-out” or similar.
I’ll just add, make sure the oil container is relatively deep and not likely to tip over and do it outdoors if possible because hot oil will ignite very very fast.
Another way is to put the oil container in another containing water and then the temperature won’t go above 212, but have the oil container raised a little so that there is water underneath it.