Being entirely contained within the headstock, and driving through the normal screwcutting changewheels, the design of the Coarse Screwcutting Attachment was unusual,  - it did not rely on an auxiliary or separate leadscrew or powershaft running down the back of the bed. The ordinary "tumble reverse" mechanism (which was contained within the headstock) was fitted with a double sliding gear which could be positioned so that it engaged with either the usual gear on the spindle (and so cause the lathe to work normally) or with a very small gear which worked in conjunction with the backgear (which had to be engaged) to provide a "reverse ratio" to that usually employed; hence, if the changewheels were set to cut 10 threads per inch, with the device engaged it would cut one thread over a distance of ten inches. The construction was such that the enormous strains imposed on the tumble reverse mechanism by moving the carriage so rapidly, over such a long distance, were removed. Besides coarse screwcutting, the system was also ideal for generating oil grooves within bearings - and the Bradford factory used a bank of these lathes for just such a purpose. The attachment was available for the 16, 21, 25, 30 and 36-inch lathes.

Section through the headstock of the 16-inch lathe showing the arrangement of gears for the Coarse Screwcutting Attachment

External view of the 16-inch headstock showing the additional control - in line with the exposed gear on the headstock spindle - used for the engagement of the Coarse Screwcutting Attachment. On this lathe the belt drive for fine-feed ran on fixed centres.