That's what I would like to know also. I have found some examples that indicate various ways but nothing definitive. One is showing a proper bayonet lashed to a pole which has some sort of metal round pin which is on the end of the pole and then through the hole with the handle lashed to the pole. Looks almost like a No III nose cap. Bamboo is mentioned in another discussion but bamboo is hollow so can't be carved to fit inside the hole. Would also require some sort of metal cap.