Why oddball screws on guns?

[fortyshooter]

Coming from a machinist point of view...why 8-40 screws for the sight mount screws on the rifle receivers instead of common 8-32??
Yes I know more threads per inch for better strength...but a sight mount??
So much for a quick little project. 8-40's hard to come by at typical walk in stores!

[BigAl52]

I know its not a local store 40 but have you thought about Brownells?

[JEBar]

so they can get folks like me to spend money on things like Wheeler Engineering Gunsmithing Screwdriver Set with Durable Construction and Storage Case for Gunsmithing and Maintenance ===> https://www.amazon.com/Wheeler-Engineer ... 314&sr=8-4

[Sir Henry]

You’ll understand when you are a little older

[Mags]

.
8-40 is very common here. Not so much 8/32.

Coming from a machinist point of view...why 8-40 screws for the sight mount screws on the rifle receivers instead of common 8-32??
Yes I know more threads per inch for better strength...but a sight mount??
So much for a quick little project. 8-40's hard to come by at typical walk in stores!

[North Country Gal]

Actually, 6-48 is the standard size used by the vast majority of brands for the thread size on scope mounts, even brands made outside the U.S. Marlin was always the oddball with it's 8-40. If you need 8-40, check mounts for Marlins.

[Grunt67]

Coming from a machinist point of view...why 8-40 screws for the sight mount screws on the rifle receivers instead of common 8-32??
Yes I know more threads per inch for better strength...but a sight mount??
So much for a quick little project. 8-40's hard to come by at typical walk in stores!

Another former machinist here. You might find a 8-40 at Lowes or Home Depot, if you have one handy, but likely they would be a socket screw head. Never had a need to check, but might be worth a look if you're close. Other than that, Brownells, etc. as someone else said. Good luck........

[Rifletom]

forty, I might have some 8-40 screws. I'll check today when we get back from church and breakfast. Pretty sure I do, but, will check.

Edit: Dang, 6-40x3/8" and 6-48x1/4". Well, we tried. About 10 each.