The Zulu Iwisa came in small, medium and large. Seems the higher in rank, the smaller the knobkerry head. (top) This is one of my large ones, about 5 in. in diameter & quite heavy. As the less likely they would be in actual hand-to-hand combat. For the Impi's Induna (Colonel) he's have about a 2in. Diameter head (3rd down). Most were around three inches in diameter (middle). I've seen a few root-ball ones rather rough, but most were smoothed like mine. I've seen a few that had conical studs screwed in like yours, but metal. Most had intricately braided wire wraps in bands, frequently now missing or damaged. Not all had the terminal increase in diameter at the end opposite the knob.
For our resident botanist: those protruding root stubs carved to emulate studs are rather regularly spaced. I seem to recall a so. pacific plant used for clubs that have such an even distribution. I believe some Fijian clubs were made from it tho I don't recall pointy ones, they had kinda flat topped ones.
The Zulu primary weapon was however the Iklwa stabbing spear, the African equivalent of the Roman gladius. Mine has the end swell, and the banding (bottom). They also used isizenze (axes, including the stabbing axe, but Shaka banned them during his reign, and they are secondary weapons compared to the Iklwa).