My brake caliper seized and chewed up my rotor. While looking for a replacement rotor, a shim kept showing up.

I've never heard of a rotor shim. Do I need one? Where does it go? What is it's function?

Thanks in advance.

 

Offset shims are used to square up rotors. Unless your hub was machined wrong or has severe rust issues you should not need one.

 

Is this the rotor shim?

 

No, that is the hub flange, you do not have shims and do not need them.