Now , with scale selected , move your mouse over the two diagonal lines of the scale tool until they turn yellow and scale down inside up to about the middle of the cylinder.This means scale with constrained proportions.You should have something like this now (see picture five).
Now create a new cylinder with radius of 2.0 and height of 1.0 this time.Go to Create>Geometry>Compound Objects and select Boolean.In case you don't know where to go , look at the picture number six.
With the second cylinder still selected choose as operation Subtraction (B-A) , press the button Pick Operand B and then give a left click on the first cylinder.This creates a hole in the first cylinder.Now you are ready!
You should have something like this (see picture seven).
This cogwheel has many uses , from using it in 3D Studio Max in a complex of cogwheels up to exporting it as .obj in order to use it in Poser as prop or make even a character with it for more complex scenes.
I hope that this tutorial was helpfull for you!