This is a plate to align the anti submarine belts on a 6 point harness with your thighs.
When used in a seat with a single cutout in the bottom, the belts will tend to migrate together. Under heavy braking or in an accident, the belts will crush your bits, and you'll want to barf in your $500.00 helmet. You'll never get the smell out of your helmet.
It is designed for the cutout in a Recaro, but may work for other companies and models.