Omegon az-baby mount

[Penumbrella]

Hi, 

I have this mount and want to know what the thread is to attach a counterweight bar. I can see a thread there through the tension knob, and a M12 threaded bolt almost works but not quite - seems like it's the right diameter but the wrong pitch. Presumably its some imperial bolt size I'm after? 

Cheers, 

P

Edit: Pic of mount attached 

Edited November 10, 2022 by Penumbrella

[Mandy D]

2 hours ago, Penumbrella said:

Hi, 

I have this mount and want to know what the thread is to attach a counterweight bar. I can see a thread there through the tension knob, and a M12 threaded bolt almost works but not quite - seems like it's the right diameter but the wrong pitch. Presumably its some imperial bolt size I'm after? 

Cheers, 

P

Edit: Pic of mount attached 

 

If M12 starts to screw in, then it is almost certainly 1/2 inch UNC which has 13 turns per inch thread. M12 is 1.75 mm pitch. The UNC thread is 12.7 mm with 1.95 mm pitch. You can normally get about 1.5 to 2 turns of M12 screw into that imperial thread before it binds.

[Penumbrella]

Super, thanks very much. I'll track down one of them and give it a go. Cheers. 

[Penumbrella]

Just to park this, I tried @Mandy D's suggestion of a  1/2 inch UNC. But no dice. 

So I emailed omegon and astroshop.eu to ask. No response from omegon themselves (yet), but the helpful chap at astroshup did reply: 

Quote

I have tried to find out the thread type myself, but it is no standard one, I am afraid - neither a metric nor an imperial one. 

The best advice I can give is to limit the telescope's weight to the given 4 kg, then a counterweight should not be needed.

C'est la Vie

 

[Mandy D]

2 hours ago, Penumbrella said:

Just to park this, I tried @Mandy D's suggestion of a  1/2 inch UNC. But no dice. 

So I emailed omegon and astroshop.eu to ask. No response from omegon themselves (yet), but the helpful chap at astroshup did reply: 

C'est la Vie

 

OK, I didn't think it very likely, as it is not so common today, but the other imperial alternative is a Whitworth thread. 1/2" Whitworth has 12 TPI compared with 13 for UNC. The thread angle is 55° instead of 60° with UNC. For threads smaller than 1/2" UNC and Whitworth will screw together, despite the different thread form, but above this they will not due to differences in pitch.

A third option that springs to mind is that it may be a metric fine pitch, which for M12 is likey to be 1.5 mm, instead of the usual 1.75 mm. This is sometimes found on vehicle fittings such as wheel nuts.