Hi, I have got some undocumented accessoiry changewheels meant for imperial threading. Tooth numbers are 39, 40, 50, 56 and 79. Mygearhead lathe has a threading drive with a fixed reduction of 0,25 and 56 teeth. The lead spindle has a pitch of 3mm, giving a factor of 0,75 for calculations, e.g. M2,5 would require 56/63 x 10/28 x 0,75= 2,5mm. Which inch threads could I make and how do I gear up these wheels?