The trapezoidal piece is supposed to go over the base of the battery.....
Thanks, guys. Yes, my battery does have a flange. So there's supposed to be clearance? That's what was throwing me...
And what about the wave washer? It's threaded onto the stem pretty tightly; does it go above the tray or below, after the stem has been threaded through?
So many questions for something that seems so simple!