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Old February 24, 2018, 05:43 PM   #1
loademwell
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Screws for guns.

OK... I am a small town gunsmith and it seems that I have so many guys bringing in older guns (grandpas) and its missing one screw.
Prime example, I Have a Bursa 9mm (think its a bursa P9 or something like that, Its in the shop). Anyhow, He only wants one screw replaced on the rear sight. (It really is just one screw) I went through all of my grab bag of parts and I don't have one screw that seems to fit it. 8x32 is about as close as I can go but its not going in.

Main question is:
Is there a way to get the right screw from the net or somthing and how do you go about ordering it?

Or can a fellow smith pull that one screw and give me the measurements?
Hate to retap it when the threads are fine.

Thanks
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Old February 24, 2018, 07:24 PM   #2
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The screw is likely metric. Try M4.

-TL

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Old February 24, 2018, 11:57 PM   #3
4V50 Gary
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Brownells has that box o' screws. You may want to buy that.

I tried restoring a museum owned old percussion fired double barrel. The hammer screw was missing so I tried to fit it. Not American, not metric. I couldn't even make a new screw on a lathe if I wanted to. I finally made a dummy screw and waxed it in place. It was a display piece only.
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Old February 25, 2018, 12:27 AM   #4
tangolima
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Some guns use non-standard threads. The mosin rifle action screws are one example, if I remember correctly. You are mostly out of luck if you can't find the exact replacement, or aren't able to make one.

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Old February 25, 2018, 03:55 AM   #5
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You can order just about any screw you need on the internet. Try ebay.
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Old February 25, 2018, 04:58 PM   #6
tangolima
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Quote:
Originally Posted by Scorch View Post
You can order just about any screw you need on the internet. Try ebay.
You can't unless you know the thread size.

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Old February 26, 2018, 11:42 AM   #7
Scorch
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Quote:
You can't unless you know the thread size.
True. But if he can't figure out how to measure thread pitch, he is in way over his head.
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Old February 26, 2018, 12:23 PM   #8
tangolima
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True. But if he can't figure out how to measure thread pitch, he is in way over his head.
It is much more difficult to find the thread specs when you are given a threaded hole. Trying a bunch of bolts is the first to do, and the op did that. If none fits, you try searching and asking on internet (op did that too).

I probably will bring the part to a industrial hardware supply store, where they have standard threads of all sorts, and try it there. Things start to go exponentially more difficult from there. There are ways, but just time consuming, and/or expensive.

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Old February 26, 2018, 12:45 PM   #9
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Quote:
The screw is likely metric
My bet for correct answer
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Old February 26, 2018, 09:11 PM   #10
Scorch
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Quote:
It is much more difficult to find the thread specs when you are given a threaded hole.
I am aware of this, I fix guns for a living. And I have to find thread pitch for blind holes with alarming frequency.
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Old February 27, 2018, 01:45 PM   #11
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Mosin rifle action screws are metric. Mind you, there's more than one standard for metric stuff. Mosin/Russian vintage stuff may not be the same metric standards as other metric standards. Absolutely will not be 8-32. That's UNC/UNF Unified Thread Standard.
These guys do Bersa parts.
https://bersa.eagleimportsinc.com/bersa/contacts/
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Old February 27, 2018, 07:21 PM   #12
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Originally Posted by T. O'Heir View Post
Mosin rifle action screws are metric. Mind you, there's more than one standard for metric stuff.
Not all of them. A lot of them are #15-32, a special thread, non-metric though.

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Old February 28, 2018, 02:33 PM   #13
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^^^ and the barrel tenons are standard 16p, V-thread....
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Old March 1, 2018, 08:04 PM   #14
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A good start is:
Numrich Gun Parts: Gun Parts & Firearm Accessories
My next stop is as mentioned Box O Screws from Brownell's and Brownells also offers screw blank kits so you can literally roll your own screws in assorted sizes and thread. That includes US as well as Metric threads.

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Old March 6, 2018, 10:01 AM   #15
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You can try Jack 1st also.

I’ve had good luck with them finding odd ball parts.


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Old March 6, 2018, 01:53 PM   #16
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This should be common knowledge for gunsmiths...

Before WWII there was no 'Standard' or 'Common' thread types.
During the 'Punitive Expedition' & WWI every company had its own threading for fasteners.
Early Colt revolvers are Ely Whitney threading, since Ely Whitney provided tooling & machining for Colt.

Cadillac, FWD, Ford and all other makers had their own threads on fasteners, which the military ran into during WWI and specified a chart of 'Common' thread types during WWII to avoid the headaches again.

Brown & Sharp was probably the most common threading before WWII simply because they made a ton of tooling used in industral applications...

There is a reason 'Gunsmith' tools are specialized, not even common screwdriver blade widths & thicknesses are common to everyday fasteners.

Now,if you are going to 'Gunsmith' without a formal education, particularly if you are going to work on pre WWII firearms, consider finding a clock/watchmaker/gunsmith screw cutting lathe.
These are normally hand powered and since you won't find a modern one it will have a bunch of the old thread cutting tools.
You can expand on the kit by picking up thread cutting tools from broken sets as you find them...
After about 30 or 40 years you will find cutting tools to makes about 70% of the threads you will run into.
The rest you have to make the tools to cut the threads as you run into them...

European firearms (with the exception of English) will have something based on the metric system, more than likely... (No guarantees)

Your average modern screw cutting lathe will do about 20% of firearms made before WWII.
There is a reason gunsmiths have very old machines they keep rebuilding, they will often cut 50-60% of screws you run into.
Then you have to find the gears to drive the cradle, which sends you on endless junk store, eBay & used machine tool broker searches...

Brownells has a 'Grab Bag' of 'Gun Screws', and sometimes places like Numrich Gun Parts will have the part you are looking for. https://www.gunpartscorp.com
Be prepared for disappointment & frustration if you don't have an exploded view & part number, which Numrich has THOUSANDS of to search.
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