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Hi all. Does anyone know what size/fitting these grub screws are? 

I'd like to add a nut/bolt/screw into the hole to attach my focuser. If possible to act as the grub screw AND to hold the mount. Or if not, i could remove that grub screw and just use it for the mount. (one side should be enough to hold tension on the drawtube) 



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After much googling and testing the grub screws, thought they where M6 with 1.25 thread.... 

But this size doesn't exist.... 

So, I americanized the size i thought it was, and found an imperial size of 1/4 20tpi.

Seems this imperial size is almost the same as the M6 1.25 which i thought it was... And its easy to source those. 

I've ordered some up and will post if they work. 

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Those screws look like they are tension adjusters and if so cannot be replaced by bolts. Is there enough thread left exposed for external bolts to hold without moving the grub screws?


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I really don't think that's a good idea.

The tension on the grub screws is critical to stop the draw tube slipping and with a heavy rig the difference between sufficient tension and cracking the ceramic bearings is less than a quarter of a turn. To achieve the correct tension and hold the bracket in place would require the bolts to be precisely the correct length - to within a few microns !!

You could always drill and tap the body of the focuser to fix into (Think resale value!) or better still make some 90º brackets and use the hold down bolts that fasten the focuser to the OTA.

I would strongly counsel against replacing the grub screws with bolts.

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I've had a good olay around with bolts of various sizes, and length. 

I have currently a temporary solution, using just one side, replaced the grub screw with a bolt and washer. The grub screws are highly adjustable to suit the tension on the drawer tube and I have managed to grind a bolt down for the right side, so it has the same tension as before with the grub screw. 

I'm waiting for my new stainless steel ones to arrive and I'll decide if I use one or two of them at that point. But don't worry.... I'll make sure its all solid and safe. 

Thanks mike

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Just a thought - why not contact Moonlite?  

I spoke to Ron at moonlite@focuser.com a while ago when I had some questions about a moonlite and he was super helpful

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