The reason propane is not used for welding (of steel) is that the oxy-propane flame is a good 1000 deg F lower than the oxy-acetylene flame so you can't reach the melting temperature of steel.Welding requires melting of the base metal.Brazing is done at a lower temp so it is possible and cutting...
socketdeveler, I may have another possible answer for your wrenchs' markings.
My earlier days working with english motorcycle and cars made before the mass changeover to the american style of fasteners left me with some wrenches made to the British Standard and Whitworth pattern.I have some by...
For some more ideas,tips,examples and questions answered take a look at ; www.practicalmachinist.com some other knowledgable people there and possibly some leads to a machine.As a home shop mechanic for 55 years and a lathe owner for 40 years I will have to say it is a very useful tool for so...