pt70 said

Pipe threads have been standardized for over 70 years and longer. Buy a 3/4'' NPT today and it will screw into a 3/4'' NPT fitting of yesteryear.
Same with nuts and bolts. Model A Fords used standard [inch] hardware in both coarse and fine threads. That's almost 100 years ago. Metric stuff is also standardized, like what you find in a hardware store. But some manufacturers chose a different 'standardized' pitch for their application. And good luck finding a replacement.
The old English cars used something called 'british whitworth' threads. Just stay away!

Ball bearings used in machinery and cars have been mostly metric since the 1940's and longer. Bearings used in old woodworking tools and lawnmowers are usually 'inch bearings' [both ID and OD are finish ground to a specification]. It wouldn't surprise me that Sears or Montgomery Ward would use a combination bearing. In most cases, the number stamped into the side of the race is still valid for a 70 year old bearing. With a set of dial calipers and a conversion chart, you can be a hero.

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