How do you order the correct length rubber for your gun, you ask? Here is the math:
Measure (in inches) the length from the band slot opening at the top of the gun, all the way down to the furthest fin on your shaft (make sure the shaft is locked in the trigger mech of the gun). From there, take that number and add it to the following equation:
Gun length x 2, divided by 3, minus 3 = 300% band stretch
Many guns are rigged with (2) 16mm Regular I.D. Power Bands with this equation.
Example - a standard 120cm speargun has an average length of 48 inches from band slot opening to the farthest shark fin. 48 x 2 = 96 divided by 3 = 32 minus 3 = 29 inches. That will give you 300% band stretch if you order a 29 inch power band for your 120cm gun. Order 2 bands for proper power on larger guns.