I was looking through the gallery today when I found this image.

http://www.myArmoury.com/albums/photo/1987.html

I have the windlass 16th century german mace that looks like this one. I would like to re-do the grip so that mine looks more like this one.

Any ideas on how to accomplish this?

Assuming that the surface is leather, I would say that that is simply a spiral-carved wooden grip covered with thin leather.

that might not be leather.... might be horn or just wood.

An easy way to get a similar look would be to wrap a thin rope around the handle, to get the spiral look, then add a thin layer of leather covered with glue. Wrap the handle with a string going in the same direction of the rope to conform the leather to the rope. Instead of carving out a spiral in the handle this is a relatively easy way to get the desired effect.