The reason I asked about the gear train is that it is all basic math. You have a lead screw with a certain pitch. Let's say it is 8 tpi, threads per inch. If you had gearing that overall made the ratio of spindle to lead screw one to one, then you would be making an 8 tpi thread. If you changed the gear on the shaft that drives the QCGB to one with twice as many teeth, then you would be cutting 16 tpi. The gears in the QCGB further change the gearing. Interestingly, the gears between the spindle and the QCGB shaft, excluding the spindle and QCGB shaft gears, all add up to zero unless there is a gear offset in the train where two gears are connected back to back and you are using one gear as the driving gear and another for the driven gear, then they count in the train. Otherwise, it does not matter if you have 12 or 100 teeth on a gear between the spindle gear and the QCGB shaft gear, the ratio will not change there. Is the QCGB missing the threading chart? If it is there, how about posting a picture of it? If not, we will need to know the model of the lathe to possibly be able to help you.