A wheel has been the symbol of Rotary since our earliest days. The first design was made by Chicago Rotarian Montague Bear, an engraver who drew a simple wagon wheel, with a few lines to show dust and motion. The wheel was said to illustrate "Civilization and Movement".
Most of the early clubs had some form of wagon wheel on their publications and letterheads. Finally, in 1922, it was decided that all Rotary clubs should adopt a single design as the exclusive emblem of Rotarians. Thus, in 1923, the present gear wheel, with 24 cogs and six spokes was adopted by the "Rotary International Association".
A group of engineers advised that the geared wheel was mechanically unsound and would not work without a "keyway" in the centre of the gear to attach it to a power shaft. So, in 1923 the keyway was added and the design which we now know was formally adopted as the official Rotary International emblem.
A detailed history of the Rotary Wheel and why it has 6 spokes and 24 cogs can be found HERE.
This article was taken from http://www.rotaryfirst100.org/history/history/wheel/index.htm#.