The threaded join is a dowel type fitting in a matching bore hole, with the male/female threads at the end in each case in order to provide an overlap section. That is how they retain strength at the joint between two, or sometimes three, shaft sections.
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....one thing i noticed from the time you posted that picture, the overlap-section from the joining part on this spear is much longer then the one on the riffe spears. dont know if it could prevent the bending on the longer spears, but sure would improve strenght....