Windows 7: What does the "Chunk" do? Difference between the progress bars?

When editing the progress bar, I was wandering what the "Chunk" image was. All it does is look like a little sliver of the "Fill" bar. I also was wandering what the difference between the "Bar" and "Transparent Bar" was.

See picture for a example.

Chuck Is the back ground for most application Progress Bar.

Are usually the backgrounds for the the Progress Bar.
copy background & Windows update progress bar background.
Buttons, Boxes & Controls > Progress Bars > Normal > TransparentBar

drive background.
Buttons, Boxes & Controls > Progress Bars > Normal > TransparentBar > <2>

The easiest way to find out what things do is to color each image in a different color and test and see what shows up and what doesn't.

Jerry

But how would I know what to run or what to look at if I don't know what it does?