Gerbruder Thiel GmbH was based, originally, in Ruhla a small town in the Thüringen area of Germany and had begun 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 became 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. In addition to production at the new factory, examples were also made by Junghans, a well-known firm of watch and clock makers in the Black Forest, presumably to use what must have been spare capacity and perhaps to get manufacture underway while the new Stuttgart building was being built. After some years the East German factory was renamed "VEB Ruhla" and a new model, the 59 introduced. With sales to all five continents, the appeal of the Thiel (and others of the same type from competing manufacturers*), was its ability to mount a number of different heads - horizontal, standard vertical, high-speed vertical, long-reach 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 to provide an in-out feed, while the tables bolted to a flat, vertical T-slotted table 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 and often without having to reclamp or realign a job.
In order to convince potential buyers of the machine's capabilities and precision, Thiel ensured that every example produced was issued not only with the usual inspection chart that mapped spindle and table alignment axes and the concentricity of rotating parts, but also a jig-bored test piece - a circular plate with four holes - this "master component" proving what the miller was capable of. In the days before electronic digital read-outs, jig boring (on other than a dedicated jig borer such as a SIP) required the use of slip gauges, dial indicators and precision rulers and, so equipped the 158 proved capable of holding tolerances within ±0.01--0.02 mm. For metric and Imperial (inch) countries machines were supplied with the appropriate micrometer dials and feed screws - the dials being especially large and beautifully engraved and the screws hardened and ground and running through long nuts in a special bronze intended to give a long and accurate life.
Ingeniously constructed, the layout of the spindle-drive system was both compact and effective: the top of the main column was machined as a slideway into which slotted a sliding ram that held a horizontal spindle fitted with (usually) a 40 INT or a No 5 Morse taper socket. The ram was, in turn, machined on its top surface to accept a second sliding housing - this able to be fitted with a number of different heads as well as an overarm (with its drop bracket) to support a horizontal milling arbor and its cutters (the cutter arbor being driven from the lover spindle).  Spindle fittings were available with a range of set-down adapters from No. 1 to No. 4 Morse, these incorporating either a draw-bar thread to hold milling cutters or tang slot for drilling work.
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To solve the problem of how to drive the spindles when their housings were moved forwards and backwards (to provide lateral travel to the cutter), the topmost gear of the column-mounted speed-change gearbox was made very long and a small gear, fitted to the first of the overhead rams, allowed to slide along it. In turn, this gear protruded above the top face of the casting so that a splined shaft, held within the uppermost ram housing (and connected to the head at the front end by bevel gears), passed through its centre and allowed the gear to slide as the head was moved to and fro.
Besides normal horizontal and vertical milling operations, all models were available with a range of accessories to cover slotting, jig boring, jig grinding, spiral milling and punch milling. In respect of these operations, an important part of the machine's versatility was dictated by the multi-angle, swivelling and tilting table and indexing attachments; a machine with just the plain table and standard vertical head available remained very useful, but it was not possible to enjoy, in full, all its ingenious capabilities.
Drive System
Arranged to drive both the milling spindle and the feeds to the head and table, the main motor  fitted to the standard 158 was a single-speed, 3-phase, 2.2 h.p. 1500 r.p.m. type mounted inside the column at the back with drive by, at first 2 and then later 3 external V-belts (guarded by a full-height cast-aluminium cover) to the input pulley of the speed-change gearbox. Positioned in the column below the spindle-speed gearbox, the table and head-feed gearbox (on the ordinary version) 158 had eight speeds that gave feed rates (for horizontal, vertical and head in-out travels) of  9.5, 16, 25, 32, 45, 90, 100 and 160 mm/min. On all models the gears were hardened and ground, ran on multi-splined shafts and were lubricated by an oil bath.
Although the table feed rates were independent of the spindle-speed settings (any combination of speeds and feeds was possible), the arrangement could not provide a "rapids" travel and, to allow this, Thiel offered another version, the 158S, a type equipped with a separate motor to run the feeds' gearbox while also providing a rapids feed rate of 900 mm/min. The feeds on the S could be reversed while running and rapids selected at any moment or position simply by depressing a red-painted lever - simply releasing the lever stopped the feed. Table feeds were engaged by a pair of long levers, one positioned at each side of the knee and so allowing operation from either end of the table--or even from behind. Automatic table stops were, of course, provided and all drives protected by easily accessed shear pins. Table travels (which were not shortened by use of power feeds as on so many other makes) were 310 mm left to right and 400 mm vertically; the in and out feed (provided, of course by the ram head), was 200 mm. Feed screws on all three exes were precision ground, ran though substantial bronze nuts and were turned by large handles that provided exactly the right degree of "feel". Micrometer dials were huge, finely engraved, satin-chrome finish and equipped with vernier scales. Built-in steel rulers were provided for each axis of movement which, in combination with the standard-fit holders to accept dial-test indicators and gauge blocks, allowed high-precision measurements by co-ordinates to be made, independent of the feed-screw readings.
Provided in a correct geometric progression, the 12 spindle speeds spanned a useful: 60, 80, 106, 140, 180, 240, 320, 470, 536, 700, 920 and 1200 r.p.m. Fitted with a sliding commutator, when switched off the motor provided a braking action that stopped all rotating feeds - as there was no idle time to the stop point, safety was considerably increased. Motor control for start, stop, brake release and jog was by push buttons with reverse selected by a separate lever. Case hardened and ground all over, the horizontal spindle ran in high-precision taper roller bearings that provided both excellent support and an easy means of adjustment.
Heads
Although the range of heads was not as wide as that offered by Deckel, a good basic range was available with, for horizontal use, an overarm and drop bracket to hold a milling arbor - both being supplied as part of the standard equipment. Also provided with each new machine was a 360° swivelling milling and drilling head, this being powered by the machine's own drive system and fitted with a No. 40 INT nose with a collet capacity of 25 mm. The quill travel was a reasonable 90 mm (and it was possible to space the centre line of its cutter a maximum of 700 mm away from the inaner face of the column). 12 speeds were provided, these being geared up from the horizontal drive to give a useful: 90, 120, 160, 210, 270, 360, 480, 705, 805, 1050, 1380 and 1800 r.p.m. Speed changes were made by three concentric dials on the columns right-hand face, this modern arrangement (as first used on Cincinnati "Dial-Type" millers) replacing the externally-mounted box with a pair of quadrant levers used on the Model 58.
To aid the drilling of small holes and the use of tiny milling cutters, a special 0.5 to 5 mm collet capacity head was available with a second spindle mounted parallel to the first and geared to give 6 useable speeds of 1720, 2240, 2920, 3840 and 5000 r.p.m. The maximum quill stroke by lever (no fine feed by handwheel was fitted) was 40 mm.
When a lot of jig, or high-precision boring or drilling was envisaged, a special automatic down-feed head (Attachment N. 7) was provided. This could be swivelled through 90° each side of vertical, had a spindle with a No. 5 Morse taper nose socket, a slide traverse of 150 mm (under power or by a hand lever) and 12 speeds from 90 to 1800 r.p.m. Three rates of power feed were fitted: 0.03, 0.06 and 0.12 mm/min. - all able to be engaged, disengaged or changed at will during as run
For slotting, the usual king of head was provided: this could be swivelled through 360°, had 8 stroke rates of 34, 45, 60, 78, 100, 135, 180 and 235 per minute with a stroke adjustment range from 0 to 80 mm and a slide adjustment of 40 mm.
Tables
Unlike many makers who charged extra, fitted as part of the 158's standard equipment was a  700 mm x 260 mm table that could be tilted backwards and forwards through 30° and rotated in a horizontal plain through the same angle. Other tables available at extra cost included Attachment No. 9, a special large unit 390 x 820 mm with 5 T-slots each 14 mm wide - the table able to be moved across the vertical mounting table either way by 100 mm. A similar accessory to the standard tilting table was a 800 x 270 mm unit that incorporated a screw-driven cross slide with 130 mm of travel measured by a very large micrometer dial with a vernier scale. In addition to the 30° of  forwards and backwards tilt and rotation in a horizontal plane through 30° this table (Attachment No. 12) could also be swivelled about its horizontal axis by 90°. With care, the makers claimed that setting accuracy to be within 6 minutes of arc could be achieved.
Available to fit any table was a horizontal swivel sub-table with a working surface of 130 x 800 mm with a single, central 14 mm T-slot. Amongst the standard equipment included with every Thiel 158 was a variety of equipment that allowed it to be pressed into service immediately: a universal swivelling and tilting table, a vertical milling head (Attachment No. 5) a universal dividing head (Attachment No. 1), an overarm for holding horizontal milling arbours complete with bushed drop bracket, built-in precision rulers, slip gauge platforms, 3 dial-test  indicators, complete coolant equipment with pump and piping, a standard off-set boring head, a centring device, 1 short and 1 long milling arbor to hold cutters, 1 collet, Morse taper sleeves No. 2 and No. 3, 2 collet spanners, drill chuck, 3-jaw chuck on a collet mount and with 2 sets of spare jaws, swarf tray, Low-voltage light unit with a 50V transformer, grease gun, two drain pipes for the coolant system and the necessary fixing bolts, spanners, handles, dividing tables and an instruction book..
*Proof of the type's success - the genus Precision Universal Milling Machine - is evident from the number of similar machines made in various countries including:
Austria: Emco Model F3 Belgium:  S.A.B.C.A. Model JRC-2 Czechoslovakia:  TOS FN Models England: Alexander "Master Toolmaker" and the Ajax "00", an import of uncertain origin.  Germany: Hahn & Kolb with their pre-WW2 Variomat model  Wilhelm Grupp Universal- Fräsmaschine Type UF 20 N/120 Hermle Models UWF-700 and UWF-700-PH Leinen Super Precision Micro Mill Macmon Models M-100 & M-200 (though these were actually manufactured by Prvomajska); Maho (many models over several decades)
Ruhla Rumag Models RW-416 and RW-416-VG SHW (Schwabische Huttenwerke) Models UF1, UF2 and UF3  Thiel Models 58, 158 and 159  Wemas Type WMS Italy: C.B.Ferrari Models M1R & M2R Bandini Model FA-1/CB and badged as Fragola (agents, who also sold a version of the Spanish Meteba). Japan: Riken Models RTM2 and RTM3  Poland: "Avia" and "Polamco" Models FNC25, FND-25 and FND-32 by Fabryka Obrabiarek Precyzyinych Russia: "Stankoimport 676" Spain: Metba Models MB-0, MB-1, MB-2, MB-3 and MB-4 Switzerland: Aciera Models F1, F2, F3, F4 and F5  Christen and Perrin Types U-O and U-1 (Perrin Frères SA, Moutier)  Hispano-Suiza S.A. Model HSS-143 Luthy Mikron Models WF2/3S, WF3S, WF-3-DCM & WF-2/3-DCM  Perrin Type U-1 Schaublin Model 13 and Model 22 The former Yugoslavia: Prvomajska (in Zagreb with Models ALG-100 and ALG200)  Sinn Models MS2D & MS4D  "Comet" Model X8130, imported to the UK in the 1970s by TI Comet.  Sloane & Chace in the USA produced a miniature bench version and at least five Chinese-built models have also been made, including one from the Beijing Instrument Machine Tool Works. A number of the "clones" merely followed the general Thiel/Maho/Deckel concept whilst others, like Bandini and Christen, borrowed heavily from Deckel and even had parts that were interchangeable..