What's the Screw Thread?

[Appowner]

Have a Sig Alpha2 scope mount. One of the screw heads for the rings has started to strip out the Torx socket. Anyone know what the threads for this screw are? I'm thinking it's either an 8-36 or 8-40.

And where I can find them other than Sig? My attempts at contacting them have met with confusion and being next in line for over 20 minutes. Not what I expected from Sig.

 

[fkimble@charter.net]

Take one out and go to a good hardware shop. They should have a size checker. May have to go to a machine shop to find good screws or order them online. I'd replace all of them since they don't seem to be good quality.

Frank

 

[std7mag]

I went digging on Sig's site.
The only screw info for the Alpha series was 6-32 for the Alpha 1.

 

[Appowner]

I know the thing is an 8 and I'm pretty sure it's a 36 thread (since my 8-32 doesn't work). I'm able to measure it accurately but I'm concerned as the head is smaller diam than a typical #8 head. Could Sig be using something more or less proprietary? And why would they?

Plus I have a supply of 6-32 and it definitely is not that.

Getting out is a bit difficult for me. Side effects of cancer treatment keeps me pretty much home bound. Going anywhere for any amount of time requires some advanced planning. Not impossible to do but finding and ordering on line is usually faster.

 

[Darrin]

If you can remove one of the screws you can count the threads to determine the right screw to get. It is easy with a pair of calipers. Set the calipers to 0.250 and then align the jaws up in between the peaks of the threads and count the number of peaks between the jaws then multiply by 4 to get the threads per inch.

Fastenal is a good resource because they have drawings for each fastener so you can compare it with the screw you have. Look under Product Standards.

https://www.fastenal.com/product/Fasteners?fsi=1&categoryId=600000


-Darrin

 

[Appowner]

If you can remove one of the screws you can count the threads to determine the right screw to get. It is easy with a pair of calipers. Set the calipers to 0.250 and then align the jaws up in between the peaks of the threads and count the number of peaks between the jaws then multiply by 4 to get the threads per inch.

Fastenal is a good resource because they have drawings for each fastener so you can compare it with the screw you have. Look under Product Standards.

https://www.fastenal.com/product/Fasteners?fsi=1&categoryId=600000


-Darrin

Did that the other day and came up with 36. Did it twice just now with my micrometer and came up with 40. I'm going to head to the hardware store today and see what they can tell me.

 

[Deleted Dewey]

8-36 is a production UNF screw thread but you won't find it at a hardware store. There is no reason that SIG would use a proprietary thread in such an application, it wouldn't be as profitable as using off-the-shelf.

 

[Appowner]

Finally got Sig on the phone. They're sending three of the little buggers in hopes that with spars on hand Murphy doesn't mess further with it.

As it turns out, according to CS at Sig, the screw is 8-40 by .324 inch long. Think I'll order some from Brownell's too. Never hurts to have a full set on hand.

Thanks all for the help!

 

[powderbrake]

I suggest everyone buy a thread pitch gauge for $10. That and a set of calipers will determine the screw size.

Thread pitch gauge

 

[LVLAaron]

And one of these.

Amazon.com

 

[Appowner]

I suggest everyone buy a thread pitch gauge for $10. That and a set of calipers will determine the screw size.

Thread pitch gauge

Yep! Got one. Actually two, SAE and Metric. Now if I could only find them............. MIA since we moved 5 years ago. Maybe if I bought a new one and sent it out to find the others...........?

My other hobby I use a lot of 4-40, 6-32 and smaller. I have a supply of blind nuts, regular nuts and bolts in these sizes. So if nothing else I can usually tell you what something is. Or at least what it isn't. But I've never run into an 8-40 before.

However, in my research I found out that Sig, when they started their optics division, seduced a lot of execs and engineers away from Leopold. And Leopold uses a lot of 8-40 in their rings. Why the finer thread I don't know. I'm sure some engineer made an argument for it based on his freshly minted engineering degree.

 

[powderbrake]

And Leopold uses a lot of 8-40 in their rings. Why the finer thread I don't know. I'm sure some engineer made an argument for it based on his freshly minted engineering degree.

The idea is that you should use a coarser thread on weak or soft materials, (aluminum or brass), and a finer thread on stronger materials ( like a 40 or 48 thread on a hardened receiver).

 

[Appowner]

The idea is that you should use a coarser thread on weak or soft materials, (aluminum or brass), and a finer thread on stronger materials ( like a 40 or 48 thread on a hardened receiver).

Yep! Agreed. So why did they put eight 8-40's in my Aluminum Alpha2 mount? Probably because they're used in the steel version of the mount. But that's not the one I purchased.

Actually I think the mount is a good product. I just had issues with Sig Cust Service and the fact that you have to go through them for something like a small screw. And regardless the thread on the screw, I should be able to simply e-mail them and find out what the thread is.

I waited 17 minutes being told I was next in line before someone answered. OK, that's possible. But I was in Cust Service for 23 years. Some pretty high level customers too. And had that phone call failed a letter to the CEO would have been next. My frustration level had reached the point where I was ready to find different mounts for my scope. And they would not have been Sig.