Jump to content

sgl_imaging_challenge_2021_2.thumb.jpg.72789c04780d7659f5b63ea05534a956.jpg

What size hex bolts for dovetail bar to OTA rings


Recommended Posts

Hi all. I'm wondering if anyone can tell me the name for the mounting bolts for a standard dovetail to OTA rings are called. The only reference I've found so far are M3 and M4 hex head screw/bolts and I'm still not sure on these as far as size goes, thread size, width etc.

I need two longer hex head screw/bolts for a refractor, has the standard dovetail bar and the ones I have from another dovetail bar and rings are too short. I'm only getting at best one complete turn on the thread. I need them about 20mm long.

Dave.

Link to post
Share on other sites

"M" series are standard metric thread - the number refers to the diameter.  You have to differentiate between Bolts and Screws when ordering.  Screws have thread all the way up the shaft but bolts only have thread part way along the shaft (usually about one third the length).  Heads can be "Hex or hexagon" ie a hexagon to fit a spanner, "Socket head hex" for use with an allen key.  Round head are dome shaped and have a screwdriver slot, cheese head have a short cylindrical head and a screwdriver slot.  The length of a screw or bolt should be the shaft length - but is often the overall length - better to buy longer than you need rather than trying to "add a bit" !!

Hope this helps - it can be very confusing as, while every nut and bolt is made to a "standard" there are hundreds of standards to deal with.

Link to post
Share on other sites
1 minute ago, Bizibilder said:

"M" series are standard metric thread - the number refers to the diameter.  You have to differentiate between Bolts and Screws when ordering.  Screws have thread all the way up the shaft but bolts only have thread part way along the shaft (usually about one third the length).  Heads can be "Hex or hexagon" ie a hexagon to fit a spanner, "Socket head hex" for use with an allen key.  Round head are dome shaped and have a screwdriver slot, cheese head have a short cylindrical head and a screwdriver slot.  The length of a screw or bolt should be the shaft length - but is often the overall length - better to buy longer than you need rather than trying to "add a bit" !!

Hope this helps - it can be very confusing as, while every nut and bolt is made to a "standard" there are hundreds of standards to deal with.

Hmmm, there is a lot of bolts out there that have thread all the way up the shaft.... :) I have thousands....and only a few of the bigger ones have thread only a third of the way up... the rest are fully threaded..

Link to post
Share on other sites

Cheers Roger, looking at M6 20mm but no there's mention of the length of the threaded part. atm I'm visually sizing them up by eye to get longer ones than what I have. I have round head screwdriver bolts in there now as they are a little longer but I don't like the look of them.

Thanks LB, I can also see the partially threaded ones, I don't think that would be an issue unless it would affect going through that first hole of the dovetail bar. Mine seem firm getting the threaded part though.

I'm looking at these but they don't seem to be much longer http://www.ebay.com.au/itm/4pcs-M6-x-20-Titanium-Ti-Screw-Bolt-hex-Socket-Cap-head-Aerospace-Grade-/232406159198?epid=579379141&hash=item361c7c8f5e:g:f74AAOSw4GVYQHQn

 

Edited by Aussie Dave
Link to post
Share on other sites

Are those correct in that link? They are longer than what I have by a few threads but a bit longer would be better.

M6 thread type, 20-25mm length of threaded section seems to be what I need.

 

 

Edited by Aussie Dave
Link to post
Share on other sites
3 minutes ago, The Admiral said:

I've generally bought my stainless nuts and bolts from Kay's Fasteners through eBay. You can buy in small quantities quite economically, and the service has been first rate. The pictures shown will give you a guide as to how long the thread is. http://stores.ebay.co.uk/Kays-Fasteners?_trksid=p2047675.l2563

Ian

Yes, I have used them quite a bit too.. :)

and looking at the link, they are all know as bolts, and some as part threaded bolts....so am still confused why people are saying they are screws when they are threaded all the way up.. ??

Edited by LightBucket
  • Like 1
Link to post
Share on other sites
1 minute ago, The Admiral said:

In fact Kay's do call them machine screws, rather than bolts! So it shouldn't be 'nuts and bolts'! :wink2:

Ian

 

Hmmm, fair enough but did not see that.. :)

yes just noticed that the dome headed ones are called screws, so has the shape and style of the head got something to do with it...?

Edited by LightBucket
Link to post
Share on other sites
1 hour ago, Merlin66 said:

Yes well that what I thought, a screw screws Into some substrate, and a bolt has a nut on the other side, which is exactly what I thought, nothing to do with how far up the threads go..!! So the comment about the fact that if the thread only went part the way up meant it was a screw is false.... :) bolts can have full thread or part thread....screws can also be fully threaded and part threaded....screws also tend to have a point..... :)

Link to post
Share on other sites

Only wood screws and some self tapping screws have points......

Machine screws don't have points....

(maybe the clouds will clear and persuade us to get back to more serious stuff)

 

  • Like 1
Link to post
Share on other sites

I bought the M6 25mm hex bolts or what we call over here in Australia Allen key head bolts which seem to be referred to as the same in the UK going by that site. I was only referring to them as hex screw/bolts in the opening post as that's the results I got from ebay's listings and I wasn't sure what other people knew them as from different countries. If I said Allen key, someone would of said hex. As for bolts that you use a spanner on, we just call them bolts, that's it, simple. I know you all knew what I meant, no biggy.

I think the 20mm long ones would still be a little short although I'd get a few extra full turns on them and the 25mm I'd say may be too long and I may need to pack it up with a washer or two or grind some off the threaded end. All good, problem solved, thanks everyone :) now the 4 week wait for them...

This is what I have in it now. A screw bolt both for phillips head and flat head/blade screwdrivers or what we just call here a screwdriver :icon_biggrin: (for flat head or flat blade). These screw bolts are similar looking to those that we use on our fencing here in Australia which is why I don't like the look it on my gear. It's a personal thing, I did fencing on and off for some years and that's why I want them gone.

597a42559ee79_Antares150mmFracScrewBolt.jpg.b7c4ddc6a761e4fdaf0a08020c78aaab.jpg

 

Edited by Aussie Dave
typo
Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.