With every thread or feed selection made by rotary levers (and a consequent absence of sliding controls) the oil-bath lubricated screwcutting and feeds box, with its hardened gears, could be completely sealed against the ingress of dirt and swarf. By using just the ordinary set of changewheels the box was able to generate 63 English pitches (from 96 to 13/16 t.p.i.) and 35 metric (from 0.45 to 40 mm pitch) - a range greatly superior to the 38 English and 27 metric of the Colchester Mastiff. The sliding and surfacing feeds totalled 54 from 0.003" to 0.252" per revolution of the spindle on longitudinal travel and from 0.0008" to 0.064" on the cross feed. With a different changewheel set on the quadrant arm a complete range of Diametral and module pitches could be produced and the 5-segment screwcutting chart included these thread sets in its layout. .

With its double-wall construction, oil-bath lubrication and ingenious mechanical design the all-helical-geared apron was well engineered for its task - and used throughout the Celtic range. The drive shaft from the gearbox transmitted its power through a worm and wheel to a shaft that passed vertically though the centre line of the casting at the top of the shaft a double-sided dog clutch (operated by a combined selection and engagement quadrant lever that pivoted from the centre of the apron's front face. Although the whole apron was a robust and reliable piece of engineering its feeds engagement mechanism suffered from the usual drawback of all quadrant-lever operated systems: the awkward double action of pulling out the location plunger and swinging the operating arm sideways meant that an instant (and certain) disengagement of the feeds was impossible. A simple flick-in-and-out lever, preferable working in a vertical plane between fixed positions (and through some sort of overload protection) would have been much preferred in this situation..