Gerbruder Thiel GmbH was based, originally, in Ruhla a small town in the Thüringen area of Germany and began as makers of pocket, wrist and toy watches and general metal products. The development of their famous machine tools began in the early 1900s, the initial aim being simply to supply their own factory with more efficient methods of production. Although the new products included a series of unique and long-lived filing and sawing machines, together with a specially developed metal cutting bandsaw, it was for their range of superb, very high quality universal millers that they were to become best known. The earliest such type, built in 1906, was intended for the manufacture of punches but by 1914 had developed into the much more useful and ingenious "Duplex" (the term indicating that the cutter spindle could be arranged anywhere from vertical to horizontal and the machine used for a variety of tasks). However, Thiel were not the only makers of such a model and in the United States Van Norman manufactured their own uncannily similar type, also called a "Duplex" (shown right, below the Thiel Duplex). Van Norman were handled in Germany by the well-known agents Schuchardt & Schütte, numerous examples appearing in their catalogues from 1899 to 1914. Hence, Thiel would have had the chance to see early examples of the type and either copied it, or were inspired by the design to make their own version. In addition, from the late 1800s onwards America had taken the world lead in outright production numbers and innovation in the machine-tool field - surely further circumstantial evidence that the German design sprang from an American drawing board.
By the early 1930s the very fine "Duplex 58" was in production - in which form the arrangement of its various components and controls provided such versatility that the success of the type was finally guaranteed.  At the end of WW2, in 1945, Thüringen fell under Russian control and the works directors, the designers and many workers fled to West Germany where a factory was established at Leinfelden, near Stuttgart, In Ruhla the remaining workers restarted production (with some modifications) of the pre-war Duplex 58 - while in the West a new machine, the 158 was designed and built. It is also reported (but not confirmed) that Junghans, a firm of watch makers in the Black Forest, also built the Duplex 158. After some years the East German factory was renamed "VEB Ruhla" and a new model, the 59 introduced.
Heavily revised, the Type 158 had increased rigidity, had improved table travels, a wider speed range, built-in motor(s), improved electrical and safety controls, independent drive of spindle and table feeds, fixed dowelled positions for attachments and tables and hardened and ground feed screws. However, many accessories could be swapped over from the 58, as could collets and other spindle-nose fittings.
Following the 158 was the The success of the "Universal Precision Miller" lay in ability to mount a number of different heads - horizontal, standard vertical, high-speed vertical and slotting - in combination with a variety of tables - plain, plain-tilting and compound swivelling. All the heads could be driven backwards and forwards across the top of the main column, by a handwheel working through reduction gearing, to provide an in-out feed, whilst the tables all bolted to a flat, vertical T-slotted knee equipped with power longitudinal and vertical feeds. By juggling the choice of heads and tables, and utilising other accessories, a skilled technician was seldom defeated in his attempts to produce the most complex of milled and drilled components - and all to a very high standard of accuracy.
One drawback of the 158 - and similar machines by other makers - was the need to employ a number of attachments including plain, and multiple swivelling and tilting universal tables and mount on them such accessories as rotary tables and diving heads. This fragmented approach meant that the operator had to spend unproductive time mounting and dismounting the fittings and realigning workpieces, etc. Hence, after considerable development work, Thiel introduced the 162, a machine "complete in itself" and not requiring any additional attachments or tables to function to the maximum of its great versatility. The 162 has just one main spindle, one table and with the surfaces of all jobs able to be machined in one setting - the aim of the design being to speed up the production of difficult workpieces that required finishing to a high degree of accuracy - mould, tools, fixtures, jigs, one-off complex jobs and small batch production work. The writer can confirm the success of the 162, a friend having one in his small machine shop devoted to high-class work for the aerospace automotive sectors. As nearly every job is a one-off and unsuited to being produced on a CNC machine, he would not be without it..