Can anyone identify this horn?

I'm hoping someone can ID this horn. Also, what does the large flathead screw in the center do if anything?

 

the screw may adjust the tone or be a mounting point

 

Yeah, I think it may adjust the tone. Any idea what year it's from? Or what vehicle(s) it went on.

 

Not sure what year,would assume 6 volt.The screw most likely adjust the diaphram inside this will make a difference in the noise but as the horn vibrates the diaphram has a small (for lack of the correct term) nipple that rubs against a gear the vibrates the diaphram through use the nipple wears down.and they would have to be adjusted to function properly

 

loosen jam nut,

With that pitting it might not be so easy.

then.
turn screw to adjust vibrator.

 

That's what she said... Too Soon?

Cheatercarl

 

Lube will always help!

 

Thanks for all the input fellas. I have hooked it up to my 12v truck and it worked fine. Hope that was not a bad thing to do? I'm going to bead blast it tomorrow and see how it looks underneeth.

 

A 6v horn will work very well with 12v, louder and higher pitched. Long continuous operation might burn it out, but I have on Nash hot rod that has been working a couple of years now. It has a unique sound........