ISO 4231:2016 is a supplement to ISO 2568 and ISO 4230 and specifies the dimensions of hand- and machine-operated circular screwing dies intended for production of parallel pipe threads, G series, in accordance with ISO 228-1. The general dimensions of these dies (diameter, thickness and fixing dimensions) are in accordance with ISO 2568 so as to permit the driving of hand-operated dies with the aid of the die stocks defined in that document.