'''Arnold''' (''Metallspielwarenfabrik K. Arnold GmbH & Co'') war ein deutsches Unternehmen, das Blechspielzeuge und Modelleisenbahnen, hauptsächlich in Spurweite N, herstellte.

Das Unternehmen wurde am 4. Oktober 1906 in Zweiten Weltkrieg wurden alle Nürnberger Produktionsstätten zerstört. Es blieb nur der Zweigbetrieb im oberpfälzischen Mühlhausen erhalten, in dem die Produktion nach Kriegsende wieder aufgenommen wurde. Durch den allmählichen Rückgang des Blechspielzeugs verlegte man sich Ende der 1950er Jahre auf die Herstellung von Modelleisenbahnen. Im Jahr 1960 wurden erstmals Modelle in der Spurweite N (N für "''N''eun Millimeter") auf der Maßstab 1:200 präsentiert. Ab 1962 wurden die Modelle von "''Arnold Rapido''" im auf 1:160 geänderten Maßstab gefertigt. Dieser wurde im Jahr 1964 für die Spurweite N in NEM 010 international genormt. Nach vielen erfolgreichen Jahren musste Arnold 1995 italienischen Mitbewerber Hornby Plc. Teile von Rivarossi und u. a. auch den Markennamen Arnold. Seit 2006 sind wieder Modellbahnprodukte unter dem Namen Arnold im Handel erhältlich. Die Produktion erfolgt in China.

Arnold produzierte fast ausschließlich Modelle in Spur N. Erst in den 1990er Jahren wurde die Produktpalette um wenige Fahrzeuge in der Nenngröße TT erweitert.

Founded in 1906 by Karl Arnold in Nürnberg, '''K. Arnold & Co.''' began its life producing tin toys and related items. They produced an extensive line of model ships, doll house items and other toys.  In 1935, K. Arnold & Co. hired Max Ernst as their managing director.  Ernst, not to be confused with the German realist artist of the same name, was a significant factor in the future of Arnold.

Nürnberg was badly damaged by allied bombers during World War II, and, at the end of the war, all of the Arnold facilities were in ruins.  Postwar production continued at a facility in the Upper Palatinate (OberPfalz), with the company beginning its slow recovery with the manufacture of window hardware. The postwar operation of the company was under the direction of Max Ernst and Ernst Arnold, son of Karl Arnold. The factory buildings in Nürnberg were rebuilt and the Arnold Company continued to grow.

In the postwar period, smaller HO/00 scale became the “small” scale.  In the late 1940s and 1950s, TT scale was the “small” scale, allowing for realistic model railroad displays being situated in relatively small areas. Three companies led the TT revolution, H.P. Products of Indiana, USA, Tri-ang of the United Kingdom and Rokal of West Germany.

But TT-Scale was not to be the smallest scale in model railroading. Led initially by Trix of Nürnberg, there was a movement toward an even smaller scale. Both companies experimented earlier with “floor toys”, unpowered model trains designed to be moved about by child power.  Lone Star dropped by the wayside after a period of time, but Trix continued experimentation and development of what would be their electric powered Minitrix product line. Arnold was to come up with a workable solution, also. The introduction of Arnold rapido was from scratch because nothing like this had been done before. Arnold was literally establishing what would become N scale.  This is not to say that it was the sole developer of N, but Arnold Rapido was there first.

Although Karl Arnold’s son, Ernst, was involved with the company, several sources cite the presence of Max Ernst (who remained as Managing Director for over forty years until 1976), as the prime mover behind this new product line. Ernst has been described as a dynamic businessman, the person most responsible for the introduction of the Arnold Rapido product line.  Karl Arnold passed on in October, 1946, leaving his son and Herr Ernst as principals in the Company. Much later, an Arnold Sales Manager, Ferdinand Graef, would marry Max Ernst’s daughter, Sonja, keeping the Arnold company as a family operation.  It would continue to be so until 1995.