Personally, I have had better service with the drill bit style of spot weld cutter than I have with the toothed ones. I keep breaking the teeth on the toothed ones. The drill bit type are available in 8mm and 10mm. I keep both since they are cheap. And they like to be turned slooooooooowwwwww so as to not build up heat. I can use a drill bit style one for a long, long time because it doesn't have teeth to break off.

https://www.ebay.com/itm/10-mm-COBALT-SPOT-WELD-CUTTER-WELDER-DRILL-BIT/230756723524?epid=1258453770&hash=item35ba2c2b44:g:FlYAAOSwd4tT82yr

Master, again and still