This die set includes 5 pieces of dies:
#20 Cap Die
#18 Cap Die
#16 Cap Die
#18/20 Stud Die
#18/20 Socket Die
With this 5 pieces die set, you will be able to apply both size 18 and size 20 snaps as well as size 16 caps with size 18/20 studs and sockets since size 16 caps fit size 18/20 studs and sockets.

You will not be able to use this die set to apply size 16 studs and sockets.