"Any 7-speed Shimano Hyperglide Freehub will actually work with 8 sprockets, without any modification! What you need to do is to use 8 of the sprockets from a 9-speed cassette, with the 9-speed spacers."

"To make this work, you'll also need to use a 9-speed chain and shifters. Your old 7-speed derailer should work OK if it isn't too badly worn. The limit stops on the derailer will cause the useless 9th position on the shifters to be locked out, so this will work as a perfectly normal 8-speed rig." - Sheldon Brown

Am I reading this correctly? To convert my Shimano 105 7-spd wheel to 8-spd, I need a 9-spd cassette minus one cog and a 9-spd shifter. Then redish the wheel to bring it to center. And, my 7-spd 105 RD should work. I don't understand what he means inthe second line, "a 9-speed cassette, with the 9-speed spacers." What spacer is he talking about?