Hi Paul. I’m always interested by those threads ! Can you pls post pictures ?
Hi Patrick, I will in a bit - I’m in the process of doing a minor bit of restorative work, but will be happy to at some point soon.
Edited to add: Here’s a couple from the ebay listing…
http://japanese-vintage.org/images/japanese_ceramic_2015_feb_0833.jpg
http://japanese-vintage.org/images/shamisen_2015_feb_102.jpg
The doukake is on the wrong side… I didn’t take the picture 
These measurements can be tricky because not everyone measures the same way. For example, do you measure the sao thickness at the widest point of the cross section or just at the face. Not all sao have the same profile cross section. A better measurement would be the overall length. Hosozao tend to be shorter by several cm, although there are some shorter chuuzao also.
Given that, for comparison my thinner neck chuuzao jiuta shamisen has a dou 20.5cm x 22.5cm measuring the outside of the dou. The neck is 26mm at the tenjin. At the bottom end it is 27mm for just the face at 30mm entire width.
If we are measuring apples to apples, yours is likely a nagauta style shamisen.
Overall length of mine from the bottom of the sao peg to the top of the tenjin is 98-100cm +/-. From nut to typical bridge position is 77.5cm… width of the sao at the centre of the middle section (approximate centre of the sao) is 27mm…
I don’t dispute that its Nagauta intended, that would be right for its style and vintage. The shamisen knows not it’s name…
This youtube video shows an similar instrument to mine, in the same vintage period…
A jiuta will be 99cm. The problem with measuring is the different typical size shamisen only vary by a few centimeters so your measurements have too much variability. I do agree with you that from the pictures, this looks more robust than a typical hosozao. Regardless it is a very nice looking kouki shamisen.
Enjoy
P.S. The doukake are usually well fitted to the dou. Sometimes the doukake will have writing on it telling you the type of shamisen it is meant for.
One thing that has confused me in talking about shamisen sizes is the term “neck thickness”. Is what is meant by thickness, actually the width of the sao (face width), or is it actually referring to the thickness - the dimension from the face to the back of the sao…?
width
Do you think the measurements could have changed in 60 years?
It seems that the traditions of classical shamisen music don’t change much (?) in the sense that eg. nagauta hasn’t received any distinctly new compositions even in the 20th century, but the interpretation of the tradition has changed quite a bit.
Take the dozen (or more) different distinct styles of classical shamisen music, then the various makers of the instruments who probably don’t communicate let alone standardize that much, and likely even today you have different opinions on what constitutes the acceptable/desirable measurements of a given style of instrument.
I suppose the sao is used to categorize shamisen because it’s about the only measurement that can make sense of all the different styles and tells you something about the general character of the instrument.
A long time ago that was probably true. However post WWII the basic dimensions are fairly standard (dou size, sao length). One thing that is not standard is sao width. There are some other subtle non-critical variations for individual instruments. However shamisen makers have a range of steel templates to match the size and curvature of the various parts. A good example is that my shamisen are ~40 years old and I use a style doukake that is not strung on. It simply is pressed into place and holds by tension. They can do that because the dou are a standard size.
I don’t think most people today understand how long ago thing became machine produced and standardized. Most of my wood working hand tools are 80+ years old. Most tools made during or after WWII are considered low quality or just junk.
Most of the shamisen on Ebay are a post-WWII mass produced introductory instrument. That said they have superior wood to what one gets today for a similar quality.
I think, in all honesty, that if you could sample accurately, and to the same standard, a vast number of shamisen, you’d find a continuum of sizes from hosozao right thru to futozao-tsugaru. I think each musical genre will have advocates as to what defines it, but amongst traditionalists, there is likely only some agreement as to where the boundaries are. As a hobby, I collect musical instruments (never having been a very good musician, in truth), with an emphasis on 20th century ethnically grounded instruments. I know that like the music, the instruments vary from a perceived standard in keeping with the times and tastes. There is a tendency today to compartmentalize instrumental music, especially with instruments steeped in ethnic tradition (the banjo being a major example).
The key point is made in several Bachido posts - if you like a certain style, most shamisen will play what you like with the appropriate technique and tuning. If you are trying to aspire to a historical interpretation, then your instrument will need to be able to reproduce the desired tone when played in the “approved” technique. That will shape your instrument choice in some ways, but not all of them.
/soapbox
My original post to the forum was made to understand what I had bought. The seller had characterized it one way - it became clear that the interpretation of what it might be was maybe loose at best. None of the discussion takes away from the instrument itself. But since the instrument is not yet complete (needs a koma, strings may not be the best choice, etc), I needed guidance as to what direction to head. Experimentation will come. I can fabricate many parts easily.
Whether my shamisen is futozao, or chuuzao or hosozao is irrelevant, and while it may not be the epitome of shamisen manufacture, it is a fine instrument in its own right. It is capable of much more than I am, and for me, that is just fine.
At any rate, there’s a lot of clarity in this thread - thanks to all.
There is still a lot of misunderstanding in the US shamisen community. The instrument sizes are standardized regarding the dimensions of the dou and the length of the sao. What style music one plays with a particular instrument is different. Of course one can play violin music on a viola, but the sound and effect are different. So, yes, it depends on if you are seeking a traditional sound. I think most people on Bachido are not that concerned with this - they just want to play.
Chuuzao or not i think your shamisen is a nagauta and will fit with a white koma and nagauta strings. Of course you can change strings and coma (and even bachi) when you decide the kind of music you want to play !