Spearguns, other than pneumatic spearguns, are powered with speargun rubber (also known as power bands). The rubber is pulled back and hooked into the notch of a spear by the bridle on the rubber.
Speargun rubber comes in different thicknesses (e.g. with an outside diameter of 13 mm, 16 mm, 18 mm, 20 mm etc.) and lengths (to suit the target "gun length" being the distance between the inside of the gun muzzle to the front of the trigger). We have top quality bulk rubber, which is normally cut to size, and you make up the speargun rubber. We also have pre-made circular and euro rubbers for some spearguns. For hand spears we carry pre-made rubbers as they tend to be all the same length.
You can buy lengths of speargun rubbers that you can then use to cut and fit your own power bands. This is suitable for experienced spearfishermen who have time to spend measuring and cutting their rubbers. However if you are a beginner you will be much better off buying pre-cut rubbers designed specifically for your speargun. This ensures you have the right length rubbers for your gun and that they are made from the most effective materials.
The thicker your speargun rubber is the harder it will be to load and the more power it will give. Alternatively, you could have two thinner rubbers that are easy to load but still provide maximum power. Twin 16 mm rubbers are ideal for most kinds of spearfishing unless you are hunting marlin or large tuna which may require several power bands.
As with any rubber product you need to store speargun power bands away from direct sunlight and extremes of heat. Store in a dry, dark place and spray with silicone lube before putting them away to keep them supple.