Bungee is used for numerous things but two of the most common in spearfishing are "breakaway" systems and dive knife tethers.
A "breakaway" system is a method of hooking your shaft and shooting line directly to your float line so that when you shoot a fish it "breaks away" from your gun. (See Image)
For a break-away Spear, You simply tie a small length of bungee (about 3” loop) from the end of your shooting line loop to the shooting line release arm on your speargun. You then clip your floatline to the mono loop on your shooting line.
The other common use for bungee is to make a loop on the handle and loop under your knife sheath so you don’t lose it.
Available in (2.9mm red), and (3.2mm orange) which is better for breakaway system and 5mm which is better to hold your knife
*Sold by the foot