I'm using C&F fly boxes and I like them alot. Mine are not the system with the removable inserts. They're also not the waterproof. They're the regular c&f boxes that are a tan color with facing microslit sides. I have one with a middle page. The others have little clips on the spine of the box that look like something could get snapped in there. I don't see anything in the product line that is supposed to fit. So, to make this question shorter: what are those clip-things for in the center of the regular c&f fly boxes?

Thanks.

Diane