These protectors stay on your needles. They do fit needles from size 1 to 10. Very handy and I'm glad that I got them. I don't own any size 0 needles so I don't know if they fit size 0.
I use a point protector on the end of my dpn to indicate the beginning of a round. These are small and ro not get in the way or weigh down my needle. I really get a lot of use out of them.