I have for sale precision drive components which I purchased in the 1980's for a project that never got off the ground. These are unused and have been in a cupboard since I bought them. The manufacturer is the Thomas Mathis Company (USA). Check out their hi-end mounts at
http://www.mathis-instruments.com/. There is a small amount of oxidation on the worm, which I think would not significantly affect performance. Original instructions are included. The worm gear is 18cm (7") diameter, with a 30mm shaft. This is an excellent drive for any home machinist planning to make a precision, medium capacity mount. Price - $400 plus postage from Canberra.