Hi. In this lesson, we're going to talk about module and how it relates to gears and gear design. Now, module is expressed as D divided by N. Now, what does this mean? Well, the D stands for pitch diameter, also known as reference diameter, and N stands for the number of teeth. Divide these two values and you get the module. This explains how big or small the gear is. In other words, it's a way to quantify the unit size of a gear based on how many teeth it has. So, why does this matter? Well, you can use this parameter to determine if gears will mesh. Here, I'm showing three different gears, but the module is equivalent between all three. Here are some handy calculations that you can use if you know the module of a gear to find out the number of teeth, the reference diameter, and the reference pitch. Thank you.