This JBL shaft is for the Competition Magnum Spear Gun. The JBL740SA is 40" (1016 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. Spear Shaft has a 3 Sling Capacity and makes a great Save-A-Dive Kit item.