The legionary had two spears. One light, one heavy. The light one did not have the wooden pin. The heavy one did. Marius is credited with the wooden pin. Caesar is said to have introduced the spearhead with its rear untempered, i.e., the point at which the socketed head was attached to the shaft. In the former case, their would be a 'hinging' effect; in the latter, a 'bending' effect. The object of the spear was to disorganize the enemy formation in addition to killing or wounding the enemy. The heavy spear was certainly a throwing spear. (The Making of the Roman Army - From Republic to Empire; Lawrence Keppie.)
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The lighter spear, which was neither hinged nor untempered, might also have been a jabbing spear. A question comes to my mind in re the Marius heavy spear. Was the head socketed to receive the shaft or was the shaft beveled out to receive the head? To me, it would seem to have been the latter in order for the wooden pin to break.