seat belt extender repair extra part?

[slawless]

My seat belt extender (grabber, butler) stopped grabbing. I have read as many posts as I can find on the subject. The end piece is broken and needs to be replaced. I bought the part from ECS. When it arrived the box had the extender end, a small screwdriver and a thin piece of metal. The metal part is very thin, flexible (Spring like) and measured about 4" x 3/8". Anybody have an idea what this is for? None of the DIYs mention it.

Thanks for your help.