Hammers

While on ironmind’s website, I was looking at the grip products. One cool thing I saw were these hammer things, bassically the end of a bar that you could put weights on. It mentioned levering them and figure eighting them. It also said that swinging a hammer was a proven way to build lower arm strength. I am curious, what are these moves, levering and figure eighting. Also, can I use and olympic dumbell handel with weights on one half for this purpose, or should i use my eight pound one hand hammer?