Col,
I think the thread is M56 x 0.75 and the only ways to get a ClickLock to fit is to get an adapter made from M56 x 0.75 female to M56 x 1.0 male and then use a ClickLock made for the Synta M56 thread or M56 0.75 to M60 Vixen thread and use the Vixen ClickLock...
I am having some adapters made to do this on my FOA by Rafael at RAFCamera but those are M47 to M56. He charges around $25USD plus post.
EDIT: OOPS, nearly forgot !!! There is another way, you can take one FS60 or FS78 extension tube and cut the skinny end off till only 12mm of the barrel remains and then get the remaining stubby bit machined to 24tpi 2" SCT thread. That will end up looking like this:
Col,
I think the thread is M56 x 0.75 and the only ways to get a ClickLock to fit is to get an adapter made from M56 x 0.75 female to M56 x 1.0 male and then use a ClickLock made for the Synta M56 thread or M56 0.75 to M60 Vixen thread and use the Vixen ClickLock...
I am having some adapters made to do this on my FOA by Rafael at RAFCamera but those are M47 to M56. He charges around $25USD plus post.
EDIT: OOPS, nearly forgot !!! There is another way, you can take one FS60 or FS78 extension tube and cut the skinny end off till only 12mm of the barrel remains and then get the remaining stubby bit machined to 24tpi 2" SCT thread. That will end up looking like this:
Sounds like a lot of trouble, especially when one doesn't own a lathe ...
If you can make one up for me, I'll pay you....only if you can that is.
Matt, I am interested in obtaining a Baader clicklock for my University 2" prism. I have measured the male insert thread to be 55.6mm and 4 threads in 3mm, so assume it must also be M56x0.75. From your information the Baader Skywatcher adaptor (# 2956256) is M56x1 so have I the same problem as Col, needing an adapter between the two slightly differing threads. I wish there was some standardisation between Eastern manufacturers!
Col, if you decide to go ahead - let me know and I will get an adaptor as well.
Matt, I am interested in obtaining a Baader clicklock for my University 2" prism. I have measured the male insert thread to be 55.6mm and 4 threads in 3mm, so assume it must also be M56x0.75. From your information the Baader Skywatcher adaptor (# 2956256) is M56x1 so have I the same problem as Col, needing an adapter between the two slightly differing threads. I wish there was some standardisation between Eastern manufacturers!
Col, if you decide to go ahead - let me know and I will get an adaptor as well.
John, the adapter you need would be different from the one Col needs as on yours the M56 0.75 thread on the prism is female while on Col's Tak draw tube it is an M56 0.75 male thread on the outside.
I'm just waiting for my adapters to be completed to see how well they fit.
Ordering from Rafael is easy, you just need a drawing of the part you need.
For my second one I just sent a rough hand drawn sketch...
Col, check if your drawtube end is male or female thread. IF your drawtube is M64, but male threaded, the Baader M64 Tak clicklock will NOT work as it is a MALE thread - you'd need a female - female adapter
Confusing...
(the Sky90 also uses a coupling to step down from M64 to M55.9 to use the CAA etc.)
Here is a TKA21200 which is shown as #6 on the second of Lewis's charts as fitting directly onto the draw tube....
The Sky90 uses a step-down ring which should show as item #10 or, the FS78 should not need one....
If Cols scope has a 64mm draw tube then somewhere along the line it has had a focuser transplant..... but looking at the pictures of Col's scope, it is the original focuser (judging by the step-down from tube diameter to draw tube casing on the casting.....
Col is getting on in years and may not be able to read a tape measure
Col is getting on in years and may not be able to read a tape measure 
