Cutting takes place only on the throat and the first full tooth; the remaining threads are above centre height and act as a nut, ensuring accurate pitch. Ideal for batch work or continuous production of threaded steel bar. Coventry dies are not interchangeable. An original set of new dies must always be used together. When taken from the diehead the set of dies should be retained in its box until required again. THROAT ANGLES:20 for general work and soft steels - supplied as standard. 33 ‘B’ type for cutting brass, available on request.GRINDING DIES:Only two angles are ground on Coventry dies, the throat angle and the rake angle and in the particular case of Holozone dies only the throat angle is ground. All dies in a set must be ground on the throat at the same time and since they cannot be accurately ground by hand, a die grinding fixture must be used.MARKING & MATERIALS:Each die is marked with: diameter, pitch, type of die and gauge number. Non-standard or special dies are marked with an SD number which should be quoted when re-ordering. When a set of dies has been re-ground several times by grinding the throat angle, the height of the cutting edge rises above centre. This condition must be rectified by grinding the rake angle until the die height is correct according to the number shown on the die.