You can look at the gears that it takes to cut a thread the same pitch as your lead screw, find the ratio between your lead screw pitch and 11.5, and see if you can put together a combination that will meet or approximate closely that ratio, working from the gears that match the lead screw pitch to what you need for the 11.5. If you have a quick change gearbox on that lathe you can also use those ratios to the lead screw pitch to help reach your goal. Some people have inputted all that information into a computer program for their lathe that gives results in TPI, decimal inches, and millimeters for every possible combination, but that is above my pay grade... Is it a pipe thread? What are you making?