Something similar, but those seem to be just right for tying onto the legs of pigeons! Yes, they would work very well for geocaching.
What are called
"nano" caches are pretty popular. They are about the size you describe, and are serious buggers to find because they are usually magnetic.
I've also seen a lot of containers around the size that you find at the pharmacy counter that are sized to hold bottles of nitro. Those are considered micros.
Got my car back today, and bless it's little heart, it was just the battery.
I'll be going caching with friends tomorrow early afternoon ... and hopefully there will be time for lunch. We're going to a great area for lunching.