The Screwcutting Attachment, (No. 166) could only be supplied if it was built into the lathe when new.
A 24 tpi master was supplied as standard, but any pitch could be supplied to order.  The principal was simple, and had been used on lathes since screw threads were invented - a master thread was made to rotate with the headstock spindle and a guide, held in contact with it, transmitted the motion to a cutting tool arranged so that it could slide along the bedway and so impart a copy to material held in a chuck - or between centres.
The system was devised by Joseph Nason of New York who obtained US Patent No. 10,383 on January 3rd, 1854 for an "arrangement for cutting screws in lathes." More complex arrangements of the same type have been used, with trains of gears to vary the ratio between the master and generated threads - that fitted to the American precision Waltham lathe being a good example.