This was the last version of the Unimat to use a cast-iron base and was notable for the introduction of a rounded "step" in front of the headstock through which a simple vertical alignment pin could pass. There was also a slight bevelling of the upper corners of the headstock support - an alteration that would be reflected in the forthcoming die-cast design - and the headstock itself may also have been increased in size slightly but with corners of a tighter radius (measurements are awaited) and its milling post-retaining pin moved to a position parallel to the spindle cartridge.
Motors used on this model included the Dutch-made painted type (the large "round" version), an early example of the very much stronger and reliable U90 (but with more sculptured end caps as shown in the large picture in the 1959 brochure) and the "regular" U90 in a colour to match the lathe. However, it is known that silver-blue finished  U90 motors were subsequently sold by American Edelstaal, and Canadian Edelstaal, as replacements for use on later green SL1000s and DB200s and so confusion on this point is a strong possibility.
The early Mk. 4 had blackened steel handwheels with wasp-tail handles, a red nameplate, the Dutch 95-Watt motor and a silver-blue hammer-finish paint. Versions made in the mid years of production (as shown below) can be recognised by the use of die-cast handwheels (still with wasp-tail handles) and a red-silver-red badge. badge. The last Mk. 4 can be identified by a larger black-finished nameplate carrying the word Unimat (but no model designation) with handwheels changed yet again, this time to a turned-aluminium type (as also used on the next model to appear, the SL), with a single-line of knurling around the periphery. The motor was a U90 type and the finish either a pale grey-green hammer effect, or plain grey. However, there was a degree of overlap between the machines with even mid-production examples found (occasionally) with the early red nameplate, U90 motors and aluminium handwheels. The Mk. 4 was finished in a hammer-effect pale grey-green and supplied with the lathe were two accessories that would become very familiar in years to come: a rather light faceplate and drive dog - both in die-cast aluminium. Another fine example: boxed and unused SL1000 and DB200 lathes can be seen here