Tjin is correct about the bulky locking screw, but here is one possible exception: http://www.rei.com/product/840178/black-diamond-magnetron-gridlock-belay-locking-carabiner.

Now this is one expensive dude - thirty bucks!!! This gives me profound sticker shock. When I began climbing, biners were two bucks apiece.

What might work for a key ring is the classic oval non locker made of round stock. I have seen these used as keyrings clipped to a belt loop, etc. These are not made new anymore, but check with your climbing buddies and you might ind one. I hve some around that I don't use for climbing anymore - the gates are stcky, which might make them even better for keyrings...