I don't remember which gear I changed and because of the cold (to me) and wet weather don't want to go look at machine chart. Actually, it's a pleasant 42F outside, but after living in the S Pacific anything below 80F is freezing to this old blood. In any case, on the change gear chart, there is a 40 tooth gear that can be replaced with an 80 tooth. It doubles threading, or halves the feed rate, depending on how you calculate things. It is a "drop in" replacement to extend the threading rate by 2.00. I have found that the slowest feed rate tends to rub rather than cut for a turn or two, and then throw a chip. But that's as much my lack of skill at sharpening tools. . .
I never looked at cutting metric threads, I needed to cut 120 TPI. That was years back so I don't recall the details. But my machine is a Grizzly G-1550 (same as current G-4000) and is mounted on a Grizzly base. Everything clears, the door closes fine, and there is plenty of clearance to the chip pan. It seems that if it works for SAE threads it should work for metric. Literally everything else is a drop in change and is so marked on my thread gear chart.
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