Kanna sizing and styles.

Tsunesaburo offer what is possibly the widest range of hand planes with regard to sizes and styles in the world today. With over 20 different blade configurations in 4 different widths for hira-kanna alone, the number of possible permutations numbers in the hundreds, if not thousands.

With so many choices, it can be difficult to choose which kanna might be most suitable for any given task. In an effort to make the choice somewhat easier, and to fully explain the differences, we present the following information.

Hira-kanna general sizing conventions.

Nominal blade
Actual width
at the cutting edge
Tradional size.
overall length.
80mm (3.14")
70mm (2.75")
2 sun
1 shaku/303mm/12"
70mm (2.75")
63mm (2.48")
1 8/10 sun
9 5/10 sun/290mm/11.5"
65mm (2.56")
57mm (2.24")
1 6/10 sun
9 5/10 sun/290mm/11.5"85mm
60mm (2.36")
54mm (2.13")
1 4/10 sun
9 sun/270mm/10.75"
55mm (2.16")
48mm (1.89")
1 3/10 sun
8 sun/240mm/9.5"
50mm (1.96")
44mm (1.73")
1 2/10 sun
7 sun/210mm/8.25"
48mm (1.89")
43mm (1.69")
1 6/10 sun
42mm (1.65")
36mm (1.42")
1 4/10 sun
36mm (1.42")
31mm (1.22")
1 2/10 sun

sun (su-nn) is a traditional Japanese measure equal to 10/33m/303mm/11.94"
sun are divided into 10 bu for smaller measures, similar to the centimetre/metre or inch/feet division.
Traditional sizes in orange are anomalies, where the quoted size and actual measure do not match. Sizes in green match the quoted size with the actual measured width.

As Japanese blades are tapered in both thickness and width, becoming smaller towards the cutting edge, the 'blade width' is measured where the blade exits the body on top.

Please note that there are two widths defined as 1 6/10 sun, 1 4/10 sun and 1 2/10 sun. Confusing to say the very least, and to be completely honest, nobody can definitely say why.

So over an appropriate fish lunch, I asked Mr. Uozumi of Tsunesaburo why the same 'size' but a different 'size'?

Shaku as a measure was not fixed like centimetres or inches, depending on what was being measured, there was some variance in the defined length. The two most common definitions were the one used in carpentry, where one shaku equals 33/100m (and one sun equals 1/10 of a shaku) and the other for cloth, where one kujira-shaku is approximately 25% longer than the carpentry variant.

But I still held a puzzled look. I was aware of the kujira-shaku and it's @25% longer length, and even that it was used for cloth. (Kujira-shaku literally means 'whale-measure' and comes from the old rulers being made of baleen.) But kanna are more closely related to wood and carpentry than cloth and clothing, why would the kujira-shaku be used?

Mr. Uozumi explained that during the Meiji era in Japan, standardisation was key to establishing Japan as an industrial nation, and because cloth was a commodity, all commodities of a similar type might be measured in kujira-shaku. But changing the definition of measure for housing might cause all manner of problems, so it was left alone. As kanna got the 'standardisation' treatment as well, their sizes were from then on fixed at the now known standards for commodities, not carpentry.

It's still not ideal nor completely accurate, but it is what it is and that's the most likely reason why the disparity exists.

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