Yes, it's an eighth inch shim. A 1/16" would have been much closer to correct. I even have thinner ones used in wheel alignment that go down to a 64th inch.
Here is an alignment shim kit which is pretty handy. But they have the little handle on the top which makes them kinda funky to use on fenders and such.
Here are body shims.
I have some round ones like this as well, these don't look so much like a shim.