One important development for the Karger company was the introduction, in 1892, of their first "precision leadscrew" models, the long-lasting DL series. This came about as the result of  enquiries by Dr. Loewenherz, the director of the P.T.R. (Physikalisch-Technischen-Reichsanstalt) in Berlin, a standards organisation similar to National Physical Laboratory  in the UK. Dr. Loewenherz was working on a new metric thread system (flank angle 53°8`) for use in precision trades such as watch making and instrument production. Needing a suitable lathe on which to turn male and female micrometer screws, taps and other items needed to launch the new thread-system, the P.T.R. turned to Kärger. The lathe supplied had a 2.5 mm pitch leadscrew, a set of 17 changewheels, and could generate pitches from 0.1 to 2 mm and up to 6 mm pitch on multi-start thread. A special spring-loaded and lever-operated support was provided - to prevent work from bending as the threads were cut - and there was also a simple but ingenious eccentric-operated slide system that permitted a quick retraction of the turning-tool as the end of the job was reached. The top slide was retained by an easily released and locked cone fitting - and a degree scale provided to gauge the angle setting. Cross and top-slide feed screws were of 1 mm pitch - though as was common at the time, no micrometer dials were fitted. In addition to the spring-loaded supporting fixture, a number of other accessories were included: a centre with drive dog, 2 hollow centres, catch plate, drill chuck, a choice of stand-mounted treadle system with a flywheel or a ceiling-mounted reversing countershaft - and even three connectors for the round lather "gut" drive ropes. With a ceiling countershaft the price was 13,500 RM (Reich marks) and with a treadle movement and extra 14,125 RM. Other accessories included 7 gears to cut English threads( 450 RM), a bell chuck (150 RM), 2-jaw chuck (225 RM), a fixed steady (240 RM) and a travelling steady (60 RM).
By 1898 the Loewenherz thread-system had been supplanted by the present metric (SI) thread-system with its flank angle of 60°..
The DL Series - much modified through several versions - continued to be manufactured until the 1950s though it remained faithful, until the last, to design features employed in earlier decades..