Originally Posted by
JunkYardBike
That looks like it's only 5 speed? Were there 5 speed UG's? If it's not a UG, it's a freewheel. You need the right freewheel tool to remove it - a bike coop is likely to have it.
There were UniGlide freewheels. UG refers to twisted teeth, although it has come to mean the older style of retaining a cassette on a freehub with a threaded sprocket. I don't know if the UG freewheels OR cassettes came in 5 speed, though.