Screw pitch f guide plate on SW Esprit 100 ED

[dhmiller]

I want to mount a Stellarvue 50mm guide scope to my Skywatcher Esprit 100 ED OTA. I have the Stellarvue but even though the screws that hold the rings onto its plate fit into the screw holes on the side of the ED100, they are the wrong pitch and only screw in about 1/3 of the way,.Does anyone know what the screw pitch of the guide plate on the side of the Esprit is and/or what type of screws I need to get? (I can mount the rings of the SV right onto the Esprit because they are flat on the bottom.) I don't know the diameter of the existing screws holding the rings onto the guider plate, but they are definitely the wrong pitch. Thanks for any help.

[Bizibilder]

Not too sure of your exact kit but if the screws are about 1/4 inch or 6mm diameter then the likelyhood is some are 1/4" BSF (1/4" diameter and 26 threads per inch), some 1/4" UNC (1/4" diameter and 20 threads per inch)and some M6 (which is 6mm diam and 1mm pitch).  This problem stems from most people being metric but the UK and USA still holding onto the old imperial system.  As you have found out they are not quite interchangeable 🤨 !!

[Waldemar]

36 minutes ago, Bizibilder said:

Not too sure of your exact kit but if the screws are about 1/4 inch or 6mm diameter then the likelyhood is some are 1/4" BSF (1/4" diameter and 26 threads per inch), some 1/4" UNC (1/4" diameter and 20 threads per inch)and some M6 (which is 6mm diam and 1mm pitch).  This problem stems from most people being metric but the UK and USA still holding onto the old imperial system.  As you have found out they are not quite interchangeable 🤨 !!

Off topic, but apparently in electro technical trades the nice metric system is replaced by  AWG American Wire Gauge... Totally crazy if you ask me and very confusing... just like the above!

[dhmiller]

Thanks for the reply. Weird cause all I am seeing on Amazon are sets of metric sizes, which of course it could be. Hope I can get answer from Skywatcher, since I don't want to make a trip to the hardware store. 

[Waldemar]

Being a tech freak, I have an assortment of bolts and nuts of most sizes and types at hand. Very handy, but sometimes I have to go to a hardware store, too... Amazone is not specialized in anything, just an online supermarket.
If stargazing or -imaging is your hobby, you better be prepared to get confronted with technical issues that may cause you some headache...

Edited August 25, 2020 by Waldemar

[dhmiller]

;-). Yes, I am familiar with "technical difficulties" since I got my first Apple II in 1981 😉 Smoking hard drives, non-functioning RAIDs, buggy operating systems, and for my super macro studio, lighting and exposure and positioning and stability issues 😉  Headaches are all part of the game. (AP is just a new game ...)

The big difference these days from 1981  is the great resource of these forums and the vast range of expertise forum members have, plus their willingness to share  (also the same for macro and just about any other hobby) I do expect problems not just initially, but for as long as I pursue such hobbies.  Hopefully I can get the correct measurements form Skywatcher, but I will also just buy a bunch of nuts and bolts and be prepared.

Thanks for the advice - very true and much appreciated.

[The Admiral]

When I need a small number of bolts I turn to eBay providers who provide sensibly small pack sizes. In fact I've just received an order from Kays Fasteners via eBay for a variety of bolt sizes and threads in pack sizes between 4 and 6! The total costs are small, and free postage. A recently received William Optics dovetail has slots for M6 and threaded holes for ¼" x 20 and 3/8" x 20 !

Ian

Edited August 25, 2020 by The Admiral

[teoria_del_big_bang]

6 minutes ago, The Admiral said:

When I need a small number of bolts I turn to eBay providers who provide sensibly small pack sizes. In fact I've just received an order from Kays Fasteners via eBay for a variety of bolt sizes and threads in pack sizes between 4 and 6! The total costs are small, and free postage. A recently received William Optics dovetail has slots for M6 and threaded holes for ¼" x 20 and 3/8" x 20 !

Ian

I have used Kays Fasteners a lot of times too, fast delivery and as you say good prices.

Steve

[dhmiller]

Thanks much.  Kays is in the UK, apparently, and would probably take an extra week or so to get here. But I will scour eBay fo a domestic supplier. Looks like a variety of  1-4/20, 1-4/26 and M6  is what  I need .

[The Admiral]

15 minutes ago, dhmiller said:

Thanks much.  Kays is in the UK, apparently, and would probably take an extra week or so to get here. But I will scour eBay fo a domestic supplier. Looks like a variety of  1-4/20, 1-4/26 and M6  is what  I need .

Ah, you don't say where you are! There must be equivalent suppliers in other countries.

Ian

[Waldemar]

You will encounter M5 and the 3/8 sizes as well in the near future...

[dhmiller]

51 minutes ago, The Admiral said:

Ah, you don't say where you are! There must be equivalent suppliers in other countries.

Ian

I'm looking! Just wish I knew what I am looking for 😉

[dhmiller]

48 minutes ago, Waldemar said:

You will encounter M5 and the 3/8 sizes as well in the near future...

No doubt... Got an initial reply from Skywatcher but they thought I was asking about the finder scope, even though I said specifically I was looking for "the measurements of the guide plate that is on th OTA." Maybe second time will be the charm 😉

[Bizibilder]

Just thought that I should mention "0BA".  This is a British Association thread - so Imperial?  Not a chance!  It is 6mm diameter and 1mm pitch - so metric? Not a chance!  The thread angle of BA threads is 47 ½ degrees, metric are 60 degrees - so they are incompatible!!  

[Waldemar]

2 minutes ago, Bizibilder said:

Just thought that I should mention 0BA this is a British Association thread - so Imperial?  Not a chance!  It is 6mm diameter and 1mm pitch - so metric? Not a chance!  The thread angle of BA threads is 471/2 degrees, metric are 60 degrees - so they are incompatible!!  

Wow... those Brittons... They have to be different, don't they...

Edited August 25, 2020 by Waldemar
typo

[Waldemar]

Maybe just go to a hardware shop and let them tell you what it is and sell you a couple of bolts.
Sawing a bit off is easier then make them longer...

[dhmiller]

On 25/08/2020 at 12:08, Waldemar said:

Maybe just go to a hardware shop and let them tell you what it is and sell you a couple of bolts.
Sawing a bit off is easier then make them longer...

Haven't been inside a store since February, but ordered several different lengths of 1/4-20 and picked them up curbside. I had to use a Losmandy mount because there was no screw that fit through the rings on the Stellarvue as well as the plate on the Esprit, but got it done with a 1" 3/4", so Imperial after all.  Thanks for the help.