I purchased a 2' section of 7" galvanized steel round duct pipe and an end cap for about $10 from Lowes. I drilled a hole in the end cap to fit over the bird feeder pole and attached the duct pipe to the cap with a couple of sheet metal screws. I attached a hose clamp onto the bird feeder pole to hold the baffle in place.
The idea originated from an article I read in the December 2003 issue of Garden Gate magazine.
Below is a drawing from the magazine.
So far it seems to have prevented the Squirrels from getting to the feed.