At some point during the early 1960s (evidence points to 1964), the factory went over from an iron base to one formed from a pressure die-casting in a heavy-duty grade of zinc or ZAMAK. These new models were on sale in England by early 1965 and in the USA a little later, by April 1965. However, it is more than likely that stocks of the older cast-iron machines had not been exhausted and the two models may have been available side by side for some time. The change of material enabled the rate of production to be greatly increased and, by eliminating some machining operations (the finish and accuracy of the castings was equal to ground components) costs reduced. The use of dies enabled the appearance of the base to be cleaned up somewhat and allowed an almost full-length, vertical flat face to be used. These first die-cast machines have become known as the "Heavy" Unimat because, a little later, yet another change of material was made to either a different grade of ZAMAK, or possibly aluminium, resulting in the "Light" version. On the "Heavy" models at the point where the M6 screws retained the bed rails (at both headstock and tailstock) the casting was given two parallel grooves. The "Light" models were painted a hammer-effect green and with minor mechanical alterations only, including rather crude, cast-in degree-graduation marks on the front of the headstock. In America the very last production machines were distributed by LUX (replacing American/Canadian Edelstaal) and were identifiable by a large red name plate, U7750 motor and rather horrid plastic handwheels (similar to those on the Unimat 3) but with clear, white-painted graduations that are preferred by some owners. Unfortunately this model was not well finished and lacked the delightful detailing of earlier machines; it had, for example, a number of surfaces that lacked accuracy and a headstock spindle sleeve with a turned rather than ground-finish.