The slotted one is the one with the hole in it. It is for identification purposes. I have a few hundred pounds of head bolts and in looking through the stash, I found a few of them that were made for this as well as one that someone did themselves. I took several pics of them and they can be found at the site picture archive here:
http://devestechnet.com/Home/MorePix#headboltoiler(click to get full size)
