Your bar ends should have a stepped inner end on them to mate up to the threaded part inside the bar. If you look inside the end of your bar, there should be a metal piece that has threads in the center, and half of the circlular piece should be cut out lower than the rest. The bar end will be made the same so that when you screw in the retaining screw, you can hold the bar end and the insert in the bar won't turn with the screw.
http://cgi.ebay.com/ebaymotors/HONDA...mZ180264764548
Paste this in your address bar, it's a set of bar ends for a CBR on ebay. They've got all sorts of different styles, these have skulls on them, but they show the step design I was talking about real well. If I remember correct, I bought grips for 7/8" bars for mine. Just don't be a goof like me and force the left grip on the throttle bar. I discovered they are a little different diameter. The left bar is slightly smaller. Hope this helped. I think I confused myself.