The M400's screwcutting gearbox was able to generate both English and metric threads: 51 Inch pitches from 2 to 84 TPI and 54 Metric pitches from 0.2 to 14 mm. By the use of additional changewheels 18 Module pitches from 0.2 to 3.5 MOD and 27 Diametral pitches from 8 to 72 DP could also be produced. The 27 power sliding feeds varied from 0.04 mm to 2.84 mm per revolution of the spindle in metric mode and from 0.0016" to 0.112" in English; the power cross feed rate was arranged to be half the sliding rate. The gearbox was provided with an oil supply, circulated by the lower gears splashing into the lubricant.

The double-wall, oil-sump apron was of a completely new design and was fitted with twin-bevel gear drive (with dog clutches) to the power sliding and surfacing feeds; this feature allowed the operator to instantly reverse either without having to stop the headstock spindle. A single lever both selected and engaged the power feeds; returning the lever to its central position to stop the cut could be done without effort, no matter how hard the lathe was working. Electrical control of the spindle was primarily from a lever attached to the right-hand face of the apron, where it fell conveniently to hand and, of course, moved with the carriage as a cut was taken. An emergency-stop button and "power-on" light on the headstock was provided and both the electrical isolator and coolant pump switch were mounted on the left-hand face of the stand.

The twin-bevel gear drive (with dog clutches) through which the power-feed shaft passed can be clearly seen in this picture of the rear of the apron.