I have a dinky Benzomatic Mapp gas-oxygen welding torch for brazing little bits --- went to B&Q in East Kilbride for new cylinders but only had the Map Gas, so across to Halfords for the oxygen bottle --- got home set the job up screwed on the yellow map-gas no problem went to put on the red oxygen bottle and it wouldn't screw on.

I checked the bottle and regulator both had big arrow pointing anticlockwise and said "Oxgygen Lefthand Thread" but on closer examination the bottle was actually fitted with a right hand thread.

[Edited on 5/5/05 by britishtrident]

Oxo should be right hand thread. My BOC portapack oxygen is in a black cylinder, acetylene is left handed in a maroon cylinder.

The convention is indeed (as Pete says) for the fuel gas to have a left hand thread

I real world cylinders yes but not in the world of disposable ones --- blow lamp propane bottles are right hand thread so the oxygen has to be lefthand --- no chance of mix these up with industrial or medical gas systems the threads are ultra fine

Doh!!! What a pain in a***!

Bummer... where do you usually get them from, do they all have their own conventions?