The Potter, like most other genuine "Precision Bench Lathes" manufacturers, employed the "Chase" method of thread generation on their machines. The method involved a Master Thread (also variously known as a "hob" or "leader") mounted behind the headstock and driven through a set of changewheels. A "half-nut" pressed onto the Master Thread and conveyed its pitch, via a sliding bar connected to an adjustable toolholder, to the cutting tool which was in contact with the workpiece.
The interconnection of the cutter holder and the half nut allowed the nut to be lifted out of engagement (by a handle attached to the toolpost upright) and the cutting tool returned by hand to the start without stopping or reversing the lathe. A little additional depth of cut could then be applied by the tool slide, the half-nut rested back on the Master Thread - and the cut restarted.
Whilst this system produced absolutely accurate threads (and was especially suited to delicate operations on thin-wall tubes used to construct such items as microscopes) the length and pitch of thread that could be cut depended upon the availability of the appropriate Master - although in the case of the Potter the thread length of five inches would have been sufficient for most jobs and the eight additional changewheels supplied as standard multiplied by eight the number of threads each Master could generate. Each hardened Master Thread - they were available in both inch and metric forms - was provided with a fluted section at one end so that it could be used to "hob out" its own replacement half-nut.
To use the attachment the lathe was run in reverse for right-hand threads - with the toolholder moving from left to right. For left-hand threads the master thread and its nut were reversed, and the toolholder moved from right to left.
Unusually, unlike many of its competitors, the Potter needed neither another slot in the back of the bed, nor a special headstock casting to use the attachment, instead the whole unit was mounted on brackets which clamped to the top of the bed. A neat touch was the provision of a pad which fitted on the bed and protected it from accidental blows by the heavy hand lever.
Similar chase-screwcutting arrangements can be seen on the pages devoted to the American makers Goodell-Pratt,  Pratt & Whitney,  Ames,  Waltham Machine Works and Wade.