Brief History of the Marque
Manufactured by Cless & Plessing of Graz, 1903-1906
The firm built their own single cylinder engines and produced motorcycles of 2.75 hp to 3.5 hp, along with a 5hp V-twin from an external supplier. Most were belt-driven, but one had cardan drive. It is possible that the shaft-drive machine and possibly the V-twin were both built by Opel & Beyschlag, or, that the Noricum machines were marketed by the O&B firm under their own name. Tragatsch writes that Cless & Plessing machines were sold in the Czech part of the Austro-Hungarian empire under the Noricum brand.
Sources: GTU Oldtimerservice, Tragatsch p229