Rear brake pad stupid mistake on RT, what is this rubber grommit?

Hi guys,

I did my brake pads on my 96 r1100rt today. Wasnt difficult to do and i got away unscathed except for one stupid mistake on the rear brake pads. I started opening the caliper bolts and noticed a rubber thingie sticking out on another end of the caliper so I pulled it slightly and the entire thing popped out. I attached the pictured of the "bolt" like thing that the rubber fits onto. Anyone know what this is and how the heck I can put it back in? I tried to stuff it in and it wont go, i tried removing the "bolt" and it wont budge. The rubber "thingie" looks like a sheath of some kind except it has bulges and stuff so it looks like you are supposed to put it on the "bolt" and then put the "cover" over it .. if only i can figure out how to get the cover off. I feel like a total twit! Please help?

Thanks,
Edwin.