I am a novice at bicycle maintenance and seeking some advice from the forum. I own a 2004 K2 Zed Sport, which is my winter/ city/ beater bike. I am looking to install a Shimano CS-HG50 free hub on a 26 X 1.5 wheel, along with a 7 speed 12-28T cassette. My local bike shop gave me a spacer to install without guidance on how to install it. Sheldon Brown has a write up explaining the need for a spacer but does not explain how to install the spacer that I could see. Youtube does not show how to install this (that I could see).How exactly is the spacer to be placed? Where does it go relative to the hub and the cassette?