Description and usage
The spearhead was a piece of metal, usually iron or bronze, attached to the end of the spear (see Spear, lance). It was either placed over the end of the spear shaft like a sleeve or wedged into a split at the end of the spear shaft and secured by tying it with a cord. The spearhead was sharpened to a point.
Translation
In both of the references the spearhead is mentioned because of its exceptional size (about 7 kilograms, 15–16 pounds). The spearhead of an average soldier weighed much less. It is possible, but less likely, that the Hebrew word qayin in 2SA 21:16 refers to the entire spear, including its iron head.