The miniature hex bolts holding the valve gear to drivers on my Sunset 4-6-0 are proving to be a challenge to loosen. First of all they only protrude about .032" so conventional hand tools don't want to get hold. Measuring the head in metric gives 2.9 mm and in inch .115" neither size shows up in wrench sets in my MicroMark catalog. I hesitate to buy a $50 set of wrenches only to find they won't fit my application. I also hesitate using anything that might mangle the heads of the six bolts I need to remove. Note I also tried making a wrench using some 1/16" thick brass but the brass wants to bend instead and wouldn't break the nut lose.