I had to replace the encoder on an LX200GPS unit recently. The older version of the encoder offered by usdigital.com, E4, was no longer available so I had to use a newer version, E4P. They recommend using a spacer tool, and while it wasn't necessary, it made for a quick install. I haven't printed out the spacer because I used the one provided, but I thought it would be helpful to have a file on hand for the future.