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NexStar GPS Screw size

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#1 KDC

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Posted 22 November 2019 - 01:29 PM

I've got an older (circa 2009 or 2010) NexStar 8" GPS scope and after the Mercury transit, the screws for the counterweight system I have mounted along the bottom of the tube must have vibrated loose and so I need replacements.

 

I searched through the messages here and elsewhere and can't seem to find what screw size is needed. These are the real small screws on the bottom of the tube - I thought they were 8-32 or 10-24 but that's not right. I took one existing screw I had left to a hardware store and even the metric screws didn't seem right - they may be an M4 or M5 but the thread didn't seem right.

 

Anybody have a definitive answer on the size & thread pitch for this scope? 



#2 markb

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Posted 22 November 2019 - 02:18 PM

Just attached my badly needed CW rail finally. The GPS11s are so back heavy, I guess in anticipation of a Fastar add-on (that most folks never owned).

Mine is on a probably 2004-06 vintage GPS11, and the Phillips head screw originals were 10-24, HD has them in button heads.

Is it possible yours were bunged up a bit when they were loose? Also threads often look different due to lighting, so I press threads together and hold it up to the light to check fit. I also thread screws/bolts into a known size nut, even through a bag.

The standard metrics thankfully have obviously different threads in this pitch.

Edited by markb, 22 November 2019 - 02:20 PM.

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#3 SkipW

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Posted 22 November 2019 - 04:11 PM

Did you try to match with both coarse thread (more common) and fine thread screws?



#4 markb

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Posted 22 November 2019 - 05:46 PM

Yes but it was obviously a coarse -24. Fine is -32 and closer to the metric IIRC.

I had recently rebuilt 2 scopes with odd sizes and was pretty sure before I checked it.

When redoing scopes this year I bought several machine screw assortments, which has made thread checking much much easier.

I never got around to getting a size and pitch thread check plate. Thread pitch checkers that look like feeler gauges are around, bit I keep losing mine.
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#5 SkipW

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Posted 22 November 2019 - 06:10 PM

Sorry I wasn't more clear - my reply was directed to the OP and especially his comment about the threads not seeming right.


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#6 KDC

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Posted 26 November 2019 - 02:26 PM

Did you try to match with both coarse thread (more common) and fine thread screws?

Unfortunately, these days its tough to find places with a decent selection - I tried two places and they only had 8-32 & 10-24 so I couldn't try to compare the coarse & fine.

 

I'm going to try another local hardware store to see if they have a better selection.


Edited by KDC, 26 November 2019 - 02:28 PM.


#7 KDC

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Posted 27 November 2019 - 12:09 PM

Finally had some success at a local hardware store...part of my problem was that there was a little bit of aluminum stuck in the threads and so that was making it difficult to figure out which pitch it was. The salesperson was nice enough to clean it up and methodically go through a few different sizes with me - both metric and SAE to find the right one.

 

10-24 was way too large, so maybe that's only used on the C11s & C14s. For my 8 inch the #8-32s worked best. They were a bit too long, but a couple of washers helped. 



#8 markb

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Posted 27 November 2019 - 01:11 PM

Nothing like success!

I buy most of my hardware on EB and Amazon, usually in assortments now.

Now that you have the pitch you can order some in the correct length. I prefer the button heads for their low profile look and lack of snags, but tastes differ. SAE sizes are tougher to buy, but I was last able to get a single pitch in a length assortment.

For the big box stores, Lowe's has about twice the 'drawer' assortment compared to HD.

The service you received, though, shows the strength of going to a local shop. Pergament, subsequently crushed by Lowe's and HD, killed all our local places nearly 20 years ago.

Edited by markb, 27 November 2019 - 01:26 PM.



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