The photo above shows the fastenings and pot of oil that Shimojo san dips the huundu in before hammering them home.
But the really important thing is that the undercut of the mortise, which makes the huundu tight, does NOT run from the outer corners to the waist like on our other huundu. Instead it starts from the middle of the sloping side and runs to the waist. So in effect these huundu don't have quite the squeezing power, but this ensures that they don't stress the edge of the plank and split them. These are the details that make my mind race (and sometimes tax my Japanese) when I am doing this kind of research.
I also forgot to mention in my last blog posting that you chamfer all the edges of the huundu in order to help it get started in the mortise. We use a knife or a chisel and just quickly chamfer all the edges.
A shot of a bamboo nail with the shaku scale. It is seven sun, three bu long, just under nine inches. The node section in the bamboo creates the "head" of the nail. It is mosodake (moso bamboo) from the mainland. Shimojo san says that Okinawan bamboo is poor quality.