Taps + Dies + Threads

Trying to do a very simple job. I have threaded a length of brass tubing with an HSS 1/4 x 40tpi die. I have two bags of nuts one from supplier A and one form supplier B. Nuts "A" perfect. Nuts "B" far too tight to be of sensible use. I made a half nut "C" from some brass hexagon, using a 1/4 x 40 tpi HSS tap. Nut is far too tight. Tightened up the die and re-ran it through again, still too tight. Ran the tap through again, still too tight. Tightened the die as far as I can without something breaking and Nuts "B" and "C" still tight and nuts "A" are getting a bit on the slack side.
Of all the pieces in this puzzle I can't work out what to chuck in the bin. Maybe me? The only good news is that I haven't scrapped the part!

Try the die on a bit of solid rod, if the tube is thin walled the die may just be squashing it and then allowing it to spring back. If that is the case then either thread a rod and drill out after if the pipe is not too long or put something in the bore to prevent distortion.
Jason
PS who have you found that supplied ME threaded nuts?

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If this is what is happening, perhaps it might help if you cut the thread on a lathe first and then run the die along to complete the thread loosely first then tightening to reduce the amount of distortion to the tube.
Alan

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The answer is don't use a monkey metal die holder with a macho die...
I cut the thread again use my tail stock dieholder which is turned steel as opposed the monkey metal aldi version and all works. Except that nuts "a" are quite slack fit. Nuts "b" and "c" are fine.
Steve