I ordered two different barrette backs from my supplier, Fire Mountain Gems. They are larger then the ones that I have been using. I got them to for people with thicker hair. They are both 4 inches long. The difference is that one of them is 3/4 inches tall. I am working on designing barrettes to go on them and then put some up for sale.
This is the longer barrette that is not taller.
This is the tall barrette.
This is a comparison of the 4 inch barrette and 3 1/4 inch barrette that I normally use.