The Secret Society of Lathe Trolls

Try to avoid the thoriated kind altogether if possible.
Thoriated ones are favoured for welding due to capacity for higher currents, but plain tungsten ones do exist.

A note on safety, many tungsten electrodes are thoriated.
Commerical tungsten sharpeners (used for putting a fine point on the tungsten to weld) will collect the dust to stop you breathing it in.

SC