Mecha, Joe, Thank you. Glad you guys enjoyed the post.
Jacob
I like to make it clear that I don't post these corrections because I enjoy correcting you, want to embarrass you, or try and come across as some great world authority, because I am not. I may know a little more than the average bear, but that is about all.
I take the time to address these types of posts because I genuinely want to see people interested in the Japanese sword to learn the basics correctly.
Over the decades, I have been amazed at how little most people, actually know about Nihonto. And I am referring to people interested in the Japanese sword, not the general public. This includes martial artists, iai practitioners, knife makers and many so called collectors. The majority of this mis-information comes from forums/online sources where people believe everything they are told is true, or from word of mouth from someone they trust. This comes from their desire to learn, combined with the assumption that everyone who posts a reply or shares information knows what they are talking about.
Nothing could be further from the truth.
The best way to learn is through sword groups/shows, published material, experienced collectors and reputable dealers (NOT GUN SHOWS & E-BAY!!).
You will find this post here in the "Sword Duscussion", read it and check out the link for the beginners page contained in the post:
http://www.bladeforums.com/threads/nihonto-the-japanese-sword-basics-for-the-novice.1478064/
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One typo I wish to correct. In my first post I stated, "It is a shobu-zukuri wakizashi". I clarified it in my second post, however, I want to be sure you understand that it should have read, "it more closely resembles a shobu-zukuri inspired shape".
Here is something I am not 100% absolute on. I do not know of any criteria for this blade shape which says it can not be a bit wider in the monoucchi than at the machi. It is my understanding that shobu-zukuri (Iris leaf shape) is based on a shinogi-zukuri shape, but without yokote and they are tapered from the shinogi to the mune. Though, I have seen a couple of papered examples which did not appear to have the tapered shinogi-ji. If they were tapered, it was ever so slightly.
But, regardless this is the closest related shape to yours. Here is an example of one(Note I normally do not use examples which are for sale, but this was the only one I could dig up and it is only used in an educational capacity)
http://yakiba.com/Wak_Shobu.htm
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After reading your last post, I understand what your concern is (i think). Your concern(correct me if I am wrong) is the wider monouchi fitting through the koiguchi and the habaki still holding the blade securely. There is no doubt that it requires a more precision fit, but it will work.
Look at the example I posted yesterday of the big naginata.
http://yakiba.com/Naginata_Naotane.htm
Notice how wide the saya is at the wide end, but also look closely at the nakago end. Look too, at the habaki on the blade. See how the blade just clears into the mouth of the saya, but almost instantly begins to flare in order to accommodate the wide portion of the blade.
Making a standard shirasaya correctly requires a lot of knowledge and practice.
Good luck.
Ed