This is a block of koa wood with holes about the size of mac nuts in the shell. I use it to hold the nut as I whack it
with a hammer. The nuts are quite hard and will go zinging pretty easily.
When you first pick up the nuts (I just wait until they fall on the ground), they have a husk, which holds
in water. Once I remove the husk (usually just a light tap with a hammer), I let the nuts dry a few weeks. Drying a little
will let the nut separate from the shell on the inside. It also improves the flavor. The nuts will keep, in the shell,
for months at least. Out of the shell I don't think they keep very well. Mac nuts are good in many ways (roasted, etc.), but
I like raw mac nuts better than any other way.