Large gears have more teeth, so the
probability that a tooth will become broken or damaged is higher than
on a small gear.

That's an interesting theory. Can't think of a reason why it would be
true, though. Actually I'd think the smaller gears would be more likely
to fail sooner.

I have owned three myford lathes. The first 2 were both change gear
machines and were 50 years old. The myford gears are nice steel gears
and the only gears that showed any wear at all were the small gears
on the reversing lever.

Apparently this metric conversion can also be used to cut threads
other than metric (BA) so there must be a setup that requires 2 of
the same gears. I will cross that road when I get to it.

Right now I need to find a 40 to complete the set. The ebay seller
was clever on this auction. He stated what it was and listed the
gears that were included. I just didn't realize that one gear
was missing. I'm sure I can buy it from myford.

chuck