PowerPC :: Replacing Bottom Case Of IBook G3

I went through all the steps to change the optical drive on an old 500 MHz iBook G3, but am unable to attach the bottom case. The problem is the two long (20mm) screws near the back of the computer -- each apparently has to insert into something that looks like a gold-colored nut with serrated edges, like gears, otherwise the screws just rotate in place and don't "lock up." I'll attach a picture, but my only digital camera until I borrow one from a friend is my cell phone, so the pic won't be too good. The gold pieces fell out during the disassembly process and I can't figure out where they now go.