From this tutorial:
<style name="CustomProgressBarHorizontal" parent="android:Widget.ProgressBar.Horizontal">
<item name="android:progressDrawable">@drawable/custom_progress_bar_horizontal</item>
<item name="android:minHeight">10dip</item>
<item name="android:maxHeight">20dip</item>
</style>
Then simply apply the style to your progress bars or better, override the default style in your theme to style all of your app's progress bars automatically.
The difference you are seeing in the screenshots is because the phones/emulators are using a difference Android version (latest is the theme from ICS (Holo), top is the original theme).