What's the application for this?

[Elias Graves]

http://www.philadelphialuthiertools...-mono-long-threaded-barrel-input-jack-nickel/

Apart from the obvious use of sticking your plug in it...
What type of guitar is this used on?

 

[irishstu]

It's generally used in acoustic guitars, where there's a thick wooden block at the end that the endpin jack has to pass all the way through. Any shorter and you wouldn't be able to thread the nut on the end.

Here's what I'm talking about:

Actually I see the one you linked to is only a jack, but not a strap holder/endpin. Nevertheless it would generally be for when you have to place it somewhere where it's passing through thick wood.

 

[baimun]

It's the jack on my Taylor. The back and rim of the guitar is a hollowed out solid body, not a laminate, so it's about 1/2 to 3/4" thick all the way around. The top is a thin, acoustic top.

Actually, thank you for pointing this out... I was looking for a place to get a couple of these jacks.

 

[Elias Graves]

And I just put one in my shopping cart for the guitar I'm making. I dig the clean look on the outside.

 

[Elias Graves]

And that's an awesome looking guitar, too.