This improves on bnolan's cryptex in two ways.

First, I added bumps to the back of the "outer inner" part. This is the part that the locking rings and alphabet rings go on. Then I added cutouts to the locking ring. This makes it so the letters will snap into place, and be perfectly lined up (and stay that way).

Second, I cut out a little piece of the "outer inner" part, and added a little piece to the indicator ring. Now the indicator ring can't spin around and get misaligned anymore.

No flat version, sorry.