Installed a sub panel in an out building. Had an electrician check out my work and he said it looked good. Also was inspected by building department but my confidence in them is a bit shaken as they also approved the wiring done by another electrician who did the main meter base at the house and crossed the hot wires onto the neutrals...what a fire that would have been.

Forgot to ask the second (competent) electrician one question.
Quick background:
I have the ground bar and neutral bar isolated from one another with one on one side of the panel and the other on the opposite side. The panel is a Siemans panel which has a plastic mounting for the aluminum ground and neutral bar.
All grounds go to the ground bar and a wire then leaves that and goes outside to 2 copper rods 8 ft into the ground. I made sure the green screw was removed from the neutral bar.

So now the question: The ground bar came with an aluminum piece of strapping about 2" long and maybe 1/2" wide with a narrowed end that fits into one of the slots on the ground bar. The other end has a hole in it. Of course there were no instructions. I have a feeling it is to be installed by attaching to the ground bar and the other end is screwed to the surface of the sub panel? Since in this case the ground bar sits on plastic mounts I am guessing the whole panel box should be grounded as well since the bar is isolated by the plastic.
Any help?