They use globe motors and have a high reduction. They were originally used for satellite dish positioning. They are pretty heavy, but we took one apart and were able to take the weight down. I apologize I don't have any exact figures for that.
They do provide really nice mounting options, and the decent sized through hole offers some unique possibilities
I remember finding them for cheaper, but a google search turned this site up:
http://www.skycraftsurplus.com/index...OD&ProdID=1016