Wow - good luck in finding documentation on this machine! I believe that W/S dropped these machines from their lineup around the early 1950's. It was a line of Precision Tapping and Threading Machines which W/S got by buying the company that developed them, or at least most of the models. It was known as the Bakewell Tapping and Threading Machine. They were quite accurate - the two half-nuts or followers were threaded in their ID's by a portion of the leadscrew, so both had precisely the same pitch. As you have seen, you need a different lead screw for each pitch thread, and you cut the half nuts from the lead screw. So, you have a fine machine there. All you need now is a manual or a chat with somebody who can tell you the details of its operation.
