The set I use was manufactured by Caterpillar.
I've never purchased anything from Caterpillar. However, Dad worked there for 30 years...
I guess it may have inadvertently fallen into his lunchbox at some point.
I measured them with my expensive Mitutoyo digital calipers and for the most part they are still dead on. Some of the thinner ones have worn tips- not a lot, about .0005. Not bad for at least 40 years old and hundreds valve and points adjustments.