Bow roller extention bells

[a70eliminator]

I think thats they're called, they are used on either end of the roller to widen the "V" surface area. I was looking at a set shown in Overtons magazine for both 3" and 4" rollers. My question to anyone whom has installed them, are the caps meant to roll along with the roller? To me it looks like they would have to fit on the outside of the roller mounting flanges therefore be stationary while the roller does it's thing, My 3" roller fits snug between the flanges yet has a enough play to roll on the bolt, there would be no way the roller with the extensions would fit between the flanges so i'm thinking they would have to go on the outside of them and be stationary from the roller. I may have to post a photo of what I'm trying to say but we'll see?