Rack and Pinion MOD 1 & MOD 2 diffrence

Hey guys can anyone tell me the difference between the mod1&2 rack? is it just the case of the teeth being spaced different?

Tooth size.
MOD is metric tooth size, DP is imperial tooth size.
MOD the bigger the number, the bigger the teeth.

Mod is short for Module (metric module in this case)

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Originally Posted by http://en.wikipedia.org/wiki/Gear#The_module_system

The module system

Countries which have adopted the metric system generally use the module system. As a result, the term module is usually understood to mean the pitch diameter in millimeters divided by the number of teeth. When the module is based upon inch measurements, it is known as the English module to avoid confusion with the metric module. Module is a direct dimension, whereas diametral pitch is an inverse dimension (like "threads per inch"). Thus, if the pitch diameter of a gear is 40 mm and the number of teeth 20, the module is 2, which means that there are 2 mm of pitch diameter for each tooth.^[21]

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