Help me make my polo mallet

one of the newmarket guys introduced us to a awesome way of fixing heads to poles.

i think he used a nut-sert? (all i remember calling it is "nutsack")

worked pretty well and you could use lots of sizes of bolt

I would like to see this, I will be building my new mallet soon and looking for a good way to fix with a single bolt in the base without the chance of twisting.