Note, it appears to me that if you change the width the thumb width does not change correctly. I didn't take the time to fix it right, i just fixed it for my case. Here is what i did. Couldn't figure out how to contact the original creator.
public void setThumb(Drawable thumb) {
if (thumb != null) {
thumb.setCallback(this);
// Assuming the thumb drawable is symmetric, set the thumb offset
// such that the thumb will hang halfway off either edge of the
// progress bar.
//This was orginally divided by 2, seems you have to adjust here when you adjust width.
mThumbOffset = (int)thumb.getIntrinsicHeight();
}