This JBL shaft is for the 38-Special Spear Gun. The JBL728S shaft is 28" (710 mm) long with a 5/16" (8 mm) diameter and 6 mm threads. Having spare parts for your gun or sling is the only way to assure you won't get skunked on a spear fishing trip. Constructed of corrosion resistant 17-4 (spring) stainless each shaft is hand-tuned for alignment then heat-treated for maximum hardness to reduce flex and provide optimum energy transfer. Shaft has a 2 Sling Capacity and the Spear Shaft makes a great Save-A-Dive Kit item.