Sorry for my slow reply. With kids going back to school, I've come down ill this week.
These are solid zinc keys, as stated by balanar. Here's a picture of the back. The keys in this picture are not mine, but mine look the same. Some keys have the slots cut all the way through, others have the bounding ring. There was no perceptible difference in feel for me between the two styles. These keys fit snug on my keyboard, just like the authentic Cherry keys I have, which is great because the last thing you want is a loose key cap.
