Thanks for the input guys.
I better give some more info. The machine is missing a lot of parts, it consists of 5 cranks that hold the auger bits connected by two wooden conrods and driven by a pair of gears that give a reduction of 2.6 : 1.
There are two of the threaded rods in question and the corresponding part they engage with is missing. I think how it works is that some kind of pin mechanism engages with the coarse thread while the fine is disengaged, the crank is turned backwards and a carriage or holder brings the post into contact with the auger bit(s) at this point the coarse thread is disengaged and the fine thread engaged and the handle cranked in the correct direction and the fine thread draws the bits into the post. The bits may have been of different lengths so as not to attack the post simultaneously.
As an experiment I split a nut and warmed the sides with the oxy and bent them out to make a thread follower able to be engaged / disengaged anywhere along the length of a piece of 3/4 allthread.
The machine was rescued from the farm at time of sale some years ago by the original owners grandson. He gave it to the chap who gave it to me with a view to restoring it. My view is that it is well beyond restoration having been out in the elements for probably 70 - 80 years, and that I'd be better to attempt to build a replica. I've spoken to the grandson and it would appear that there are no known photos or any other info available about it.
I would pay to have this job done so as to get an accurate copy, and to that end would possibly be able to post the part to whoever said they can definitely do it. Or would I be better off to take it to some commercial outfit here in Perth?
Cheers,
Geoff.