Ask the spectator to remove there finger ring.
You show an old skeleton type key. You ask the spectator to try and place the ring onto the key which they are unable to do. You then place the key and ring briefly behind your back. Then you bring your hand out and show the ring is magically on the key! The ring can not come off either side. You can then hand the key and ring to the spectator and they will not be able to get the ring off either. You can repeat the process to get the ring back off.
You can use any cover like a hanky, napkin, behind your back, ect. to get the ring on and off the key.

Recommended for ages 6 an up.
Very simple to perform.