1.5” nut.

[Ukecaster]

String spacing is more important than nut width. Koalaoha has edge binding that adds extra width outside the strings. Martin tenors have very narrow nuts, but the strings are closer to the edges. So, the spacing is exactly the same as Koaloha....

Agreed, string spacing is more important.
Yes, Koaloha/Opio/Rebel all have extra space on the edges of the fingerboard (and narrow string spacing) because of those bindings, and placement of the frets inside them. With that construction, and resulting 27mm string spacing, I just can't consider buying one, although I want one, for their excellent tone and reputation. I've heard that they were considering new neck construction to allow wider string spacing, for those who want it, but they went dark on me on this, after multiple email conversations stretching back 3 years, so I gave up on them. I hope they will eventually offer the wider specs I seek, we'll see.

As far as Martin tenors, their nut width is an inexplicably small 34mm, much like an Ohana soprano, while Martin sopranos and concerts have historically been/are around 36mm. However, Martin's tenor string spacing on those 34mm nuts is wide, at about 29mm, very close to the edges. More playable for me, but still not optimal. As always, YMMV.

 

[dancephoto]

I have a Favilla soprano that has a 1.5" (38mm) nut, and an inexpensive Mahalo soprano with a 40mm nut. I'm not at home to measure spacing, but they are both very easy to play compared with previous great sounding but thinner fretboard sopranos that I have had (Martin, Kala, LoPrinzi). I am no expert on this, but I've read that many Favillas have 1.5" nuts.

 

[Pissodes]

I've heard that they were considering new neck construction to allow wider string spacing, for those who want it, but they went dark on me on this, after multiple email conversations stretching back 3 years, so I gave up on them, figuring that COVID slowed them down, or changed their plans. I hope they will eventually offer the wider specs I seek, we'll see.

It's odd that their Koalana line (2020 issue) has a 30mm G to A spacing while all others don't. Possible the edge binding used isn't as thick on those so frets are longer and string spacing greater.

 

[bearpaw]

Mya-Moe does a 1 1/2" nut width on request.

 

[Pissodes]

Loprinzi will also do a 38mm nut on request.

 

[70sSanO]

If the actual neck has enough width, the nut can be replaced and the strings set further apart.

The only issue might happen with low tension strings and only 2mm string to edge buffer. On some shapes/stretches the string might gutter off the fretboard edge.

John

 

[badhabits]

If the actual neck has enough width, the nut can be replaced and the strings set further apart.

The only issue might happen with low tension strings and only 2mm string to edge buffer. On some shapes/stretches the string might gutter off the fretboard edge.

John

or narrower if the spacing is too wide for you. Martins would pose a little bit of a challenge, though... the bottom is not flat, but angled at something like 15 degrees or so

 

[WebParrot (s2)]

The one thing I see missing from this conversation (in addition to the wisdom already honored) has to do with neck shape. Kanile'a has a very flat, shallow profile in addition to the wider nut and string spacing. My favorite. Put the same nut/string spacing on a Kala, or KoAloha and the feel is really different (again, to me) because their necks are fuller, more rounded. I have a few Antica Ukuleleria Libero, both with thin but slightly rounded necks that play really differently than my Kanile'a, however they also have very narrow and low/shallow frets. Even with a radius'd fretboard they require a lot more precision. So, I add neck profile and fret size to the comfort equation!

 

[Just a fan]

Magic Fluke's tenor fluke is almost there with a 1.45" nut.