welding thin tubing with internal threads
 

I have a project,,, where I am welding a mild steel threaded tube to
a .106 thick mild steel tab that is about 1" long. The tubing is 3/8
OD, with .280 ID, threaded 5/16 x 24.

The weld goes lengthwise on the tube, and is the full 1" long.

I am having trouble not distorting the threads in the tube when
welding. I am tig welding with a 1/16 or 3/32 electrode (sorry, will
check in the morning for sure... it is the thinnest I have) and 1/16
(also the thinnest I have)mild steel filler. I am not a weldor, but
have had some tig and mig formal training.

Machine has a pedal that varies the welding amps, and I am not hitting
it really hard at all...

I tried putting a bolt inside the tubing while welding, but that just
fused the bolt to the tube, oops.

Anyone give me some constructive, positive help please?