Grizzly G4016, Birmingham YCL1340GH, Jet 13x40, Threading Change gears.

thingiverse

My Birmingham YCL1340GH came with a 30t, 40t, and a 127/120 double gear, which allow most common inch and metric thread pitches. These additional change gears will allow you to cut nearly any pitch that exists. For example, The stock gears don't allow for 1.25mm, 2.5mm or 5mm threads. With the gears arranged 30/127 x 120/36, you can cut all of those pitches. And many more. The included spreadsheet will allow you to type in the gear tooth count in the upper right fields, and will populate the available pitches for that combination in the lever position table. Should also work for the Grizzly G4016, Shop Fox M1019, Jet Ghb1340 and any other version of the older Norton gearbox equipped 13x40 lathes with the double speed lever on the headstock.