Nimrod is a trademark. Nimrod GewehrFabrik or "Nimrod gun / rifle Factory", was the name of Thieme and Schlegelmilchs factory.
It really depends on how you define sidelock, a while back Geno posted about the T&S:
it's sidelock. BECAUSE, when you remove plates you can easily remove all lockworks after that. Its didn't attached to plates, but two axles of lockworks go through the plates.
From
http://www.hallowellco.com/abbrevia.htm"Sideplates - Decorative steel plates mounted to the sides of a boxlock break-open gun, inletted into the receiver and into the wood just behind it, to make the gun resemble a sidelock in appearance and to provide a greater area for engraving." Sideplated guns, usually, can be recognized by the lack of action pins visible in the sideplates (although some sideplated guns are built with fake pins)."
Klupp in his book "The Drilling" declares that the Nimrod action was an improvement over the A&D boxlock design.
That is a tool.





Pete