Identical in all respects to the standard Colt (and sometimes found with Clausing badges), the Vari-Speed model used an industry-standard belt-driven unit, with expanding and contracting pulleys, mounted in place of the ordinary motor on the back of the stand. The device was controlled by a handwheel, operating through a flexible drive shaft.  As a more expensive model it's possible that this version had dual inch/metric micrometer dials fitted as standard.

Colchester Clausing 1600
Often badged as a "Bantam 1600" (and in the U.S.A. and Canada as the "Clausing-Colchester 11") this lathe was also available with top speeds of 800 and 2000 rpm.
This model can be recognised instantly by its "gated" screwcutting gearbox control lever positioned in the bottom right-hand corner of the headstock's front face.  During the 1980s a special version , designated Colt, was also produced, a machine with the centre height increased to 6.5 inches, a remarkable 40 inches (1000 mm) between centres and a choice of a single-speed range from 45 to 750 r.p.m or, with double-step pulleys on motor and input shaft, two ranges of 40 to 750 r.p.m. and 120 to 2000 r.p.m. Both inch and metric screwcutting was available with a 4 t.p.i.  Leadscrew on the former and a 6 mm pitch on the latter. The standard-fit gearbox on the Colt was, unaccountably, different to that on the contemporary Bantam and instead used the distinctive joystick control lever from a Mk. 1.
In the last years of production only Bantams with an increased centre height (6.5 inches) and a top speed of 2000 rpm were offered - but these machines should not be confused with the completely different Mk. 3 Bantam, which Colchester called the "Bantam 2000" - and which was actually a Harrison M250. All models of the Mk. 2  had a useful 1.125-inch spindle bore, 0.25" greater in diameter than the earlier model..