The previous responses are correct. I just did some 1.5 mm threading on my 1127 over the last week. You will leave the half nuts engaged and then turn off the power when you are coming up to your stopping point. Then you will back out the cross slide, reverse the motor, run the carriage back to your starting point, then set the motor back to forward, move the cross slide back to zero, dial in your infeed on the compound, and take another cut. This is also what someone without a threading dial would do to cut threads.
Thanks. I have never cut metric threads....Only standard and ACME. When I get a machine, I want to be able to cut any thread I want.You will need to determine if the lathe has either a quick change gear box capable of doing both types of threading, or if there are change gears that will enable the lathe to do both. Many of the larger machines may require a single gear change to do metric. For the smaller lathes like the 1127, it is done by changing all of the gears per the charts that come with the machines. Also, you need to decide if you want a metric machine or an SAE / English machine. My 1127 is a SAE / English machine and it uses the 63-tooth gear to convert to metric. I just have to install the proper gears per the chart on the machine.