Hi Henri...I've been checking this one out and it isn't Whitworth. The only thread I have come up with so far that is 16 TPI at 1 9/16" is an American Unified thread from the 'extra fine series'...Ian
Hi Henri...It's always a dilemma with the bigger or unusual stuff..I recently spent £120 on a tap and a die to do a couple of jobs and one of them I may never use again. ...Now you've got me interested though...what is it for? ....Ian