JoeH, I don't think they are produced, but they were commonly made in the late 50's and early 60's by bending a piece of 1/4" strap in a circle. Those who wanted to be a little more sophisticated had them turned on a lathe and shrunk them on like a flywheel ring tear. I used to make them by taking a 4" pipe with 1/4" wall thickness and splitting it and driving it on the hub. The gap doesn't hurt anything. If a person wanted to he could fill in a gap from a piece cut out of a pipe.