DRP 126499 and DRGM 192052

DRP 126499 was issued to D&P in 1901 for the use of metal or other flexible material to join the two halves of stock.  Slide rules that use this patent look like any other slide rule but "DRP 126499" is usually engraved on these rules and a magnet is attracted to them.  A copy of the patent can be found on the web at http://worldwide.espacenet.com/publicationDetails/originalDocument?CC=DE&NR=126499C&KC=C&FT=D&DB=EPODOC&locale=en_EP

DRGM 192052 was issued to Dennert & Pape in 1903 for a screw friction adjusting mechanism. ( DRGM means  "Deutsches Reichs Gebrauchsmuster," not patent.  Applicability was limited to Germany for six years.  Apparently all DRGM files from before 1934 have been lost but a description of DRGM 192052 can be found in "Rechenschieber im Wandel der Zeit" by Guus Craenen and a reference to it is in "Slide Rules, Their History, Models and Makers" by Peter Hopp.)  A cutaway view of the DRGM 192052 mechanism is shown  in at least the 1906, 1914 and 1919 D&P catalogs.  The same illustration appears in the 1910 Frederick Post catalog and is reproduced here:

This illustration did not appear in the 1921 or 1922 Post catalogs.

This mechanism was also used in the slide rules that Koch, Huxhold & Hannemann made for Post from 1925 to 1930.  Koch, Huxhold and Hannemann were, all three, employees of Dennert & Pape when the DRGM was developed and, apparently, they liked it well enough to adopt it for their own use after the DRGM ran out about 1909.  As nearly as I can tell, KHH's mechanism is identical to D&Ps old mechanism--the only difference is that KHH rules use four or five adjusting screws where D&P used only three.  The illustration of the KHH mechanism in the 1925-30 Post catalogs is the exact same old D&P illustration from 1910.   (That's what led me to mis-identify the 1925-30 manufacturer of Post rules in the Spring 2011 Journal of the Oughtred Society.)

Although "DRGM 192052" rarely appears on slide rules, it is easy to identify rules that use it.  The heads of the screws appear like this:

this is a c1910 (D&P) slide rule.  Later (KHH) production had four or five screw heads.

I am indebted to Andries de Man who told me all I know about Deutsches Reichs Gebrauchsmusters--especially DRGM 192052.