Karl Townsend wrote:

Please look at this pic:
http://www.metalworking.com/dropbox/tripod.jpg

At left center is a yoke and thick disk with a bolt clamp. The yoke
and disk are grooved or racheted. I'd like to buy this component, if
possible. What do you call it? Where might you get it?

Karl

It's a "crown gear" of sorts. I don't think you'll find it stock
anywhere, but you can certainly make one on a Bridgeport with a dividing
head.