well - this one has led me on a merry chase.
It looks like I can get another variety of Oldham coupler that will do the job. The trick is to buy two couplers - one 4mm metric bore and one 1/4" imperial bore, them mix and match the two ends. They come in either set-screw or allen-screw clamp.
Can somebody more engineering-ly oriented than me give the coupler specs the once over and make sure that the alternate coupler is suitable?
Here are the links:
1.
The Ruland coupler that was supplied with the one-piece worm. Its part number is DCD10-3-4-A
2.
The alternate Oldham coupler. They come in a variety of diameters and lengths that will be suitable.
From an installation point of view I would probably prefer the set-screw ones - is there any advantage to either the clamp or set screw that I need to know about?
Thanks,
Adam