The Swagelok fitting wouldn't screw right down to the bottom and compress the copper washer. Initially, I thought it was because there was not enough straight thread on and it was coming up against the taper, but after Id got the thread put on even longer, I realised the internal thread on the Swagelok fitting didn't go right to the bottom.

I suppose you can get threaded pipe or fittings from Swagelok that would fit, but as I am making my own, I just turned the threads off about 3 mm. Now it fits perfectly to the copper washer and I can tighten it up to seal when Im ready.

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