This original self-protecting key tag from Versa Tags is still the best!  Write on with any pen or marker, then just a simple fold and it's made.  Includes chrome-plated steel rings.  Key tags size is 1 1/4" x 3" folded.  Comes 250 per box.  Available in 9 colors.  Also available in a mixed box which includes 50 of each yellow, green, white, red, and blue.