These gears are used together for inch threading on grizzlys, with your replies and other threads I've learned several possible routes to pursue. I will post my progress / lack of progress. Thank-you everyone, talk to you soon.
I would review your manual again, as it can be a bit confusing, but look at figure 62 on page 46. Inch threading, you only use the 127 tooth gear not the 120. That would cause you to have the threading problem described if you were using both. If you were doing metric threading which is shown in the next figure 63 in your manual you do use the 127 to 120 gear, but not for inch. The gears most be fixed relative to each other. If you are having a problem with the this, than I would contact Grizzly if your lathe is still under warranty. As others have pointed out, when cutting metric threads, when you disengage the half-nut and backup the carriage, you cannot using the threading dial to pickup the thread again. I think Tom Liptons example for cutting metric threads and some of the others that I tried recently are for the more experience machinist, and the results may vary based on your skill level. I tried them, found them cumbersome and easy to make an error relative to leaving the half-nut engaged. Matter of opinion and it is also machine specific.
