bill61 hit it on the head, they are for rim scrappers.
I know Fioroni makes these little devils & they arn't cheep either! Myself I use 2mm aluminum sheet & just cut them out myself, this also allows you to cut them to the width you need them as the Fioroni's don't quite reach the inner hub of all wheels.
I think they had in mind to be able to use these with all the different wheels on the market & went for a scrapper width that would work with almost every wheel!
The ones I build last about 6mo. of normal wear & tear & take about 30min. to make all 4. They work great if your running on loose sticky dirt, mud & clay!
When running in those types of conditions I'm sure you've noticed the wheels packing up, & if you have a large jump at the track with these conditions, well thats when you really notice the debris in the wheels. As that extra weight in each wheel (throws the ballance off too!) causes you to really have to ajust your driving lap after lap. This debris really effects the car while in the air, making it harder & harder to fly & land with any consistancy!
You can use pretty much any stiffer type material to fabricate a set of these & try then for yourself. I made my first set out of extra lexan & they wore out pretty quick, but it was enough for me to see how well they work!
Steve