In Illustrator, when you draw an object, apply a stroke, then scale that object up or down, you can control wether or not the stroke size gets scaled too, or stays the same. The way you control this feature is from the “Transform” palette (Window > Transform). This can be very useful for things like logos, where you want everything to look exactly the same at every size. Let's get started . . .
I'll show you an example of scaling the stroke and the object, and an example scaling the object only, but first, draw a simple shape on the artboard like below, and apply a stroke. (I used a 5px stroke)
1. Scaling an Object and the Stroke:
Open your Transform palette, and click on the options in the upper right. You need to make sure “Scale Strokes and Effects” is “checked.” It works like a toggle switch. If it's unchecked, and you click on it, the menu will disappear, and it will be checked. Open the options again to make sure you did it right.
Now that you have “Scale Strokes and Effects” active, scale your object (with the black arrow, like normal) and you will notice that not only the object gets bigger, but your stroke as well:
1. Scaling an Object, but NOT the Stroke:
Simply uncheck/deactivate “Scale Strokes and Effects” in the Transform palette…
Now, scale your object, and only the object gets bigger/smaller. Your stroke stays the same!
This feature can save you a lot of trouble keeping things consistent at different sizes, and also works for “effects” if you use those, and brush strokes as well. No trickery, just toggling an option in the Transform Palette ūüôā