I have a 2007 Audi TT 2.0 TFSI that has been sat for a while and the discs are all rusty and need replacing. I ordered some new discs from the internet and entered the registration number of my car to find ones that would fit. The new ones have just arrived and while they are the same diameter as the old ones they are not as thick. The old ones are vented whereas the new ones are solid so the old vented ones are considerably thicker than these new solid ones. Is that ok? Can you fit thinner discs or do you have to match the thickness of the previous discs?
You have ordered the incorrect discs, or the supplier has made an error.
You will need the correct vented, thicker, disc as the caliper has a « jaw » sufficiently large for the combined thickness of pads and vented disc.
If you do try to use the solid disc then the pistons could easily pop out of the caliper and you have zero brakes...
Contact the supplier and get the correct vented disc.