Tamura Nobuyoshi Shihan: Saito Sensei thought up the heavy bokken that is named for Iwama. O’Sensei usually used a magnificent, ebony bokken [that was] on the thin side, and more a Yagyu [bokken.] ….
When he was younger, I’m sure O’Sensei used something different, but when I was an uchideshi, he usually used only light bokken. He would use whatever was at hand, but his favorite bokken was long and thin – a Yagyu Shinkage, or a Jiki Shinkage [bokken]. Except for tanren, when he used a heavy, thick bokken….
There’s a famous photograph of O’Sensei with a kake full of bokken behind him. It was like that when I became an uchideshi. We used to use the dozen weapons that are there [on that kake].
– – – French language interview on the Budo no Nayami website