STEP 1
With the shaft in the speargun, measure the distance from the front notch or fin to the rear of the band eye as illustrated below.

STEP 2
Multiply this dimension by 2/3 (0.66). The result is the band length that will yield an optimum 200% stretch to 3 times it's starting length.

You may encounter differing opinions about the exact ratio to use. Some people prefer a shorter band/higher ratio. This results in more power and a slightly longer stroke but also shortens band life and may make the bands difficult to reach on longer spearguns. On the other hand a smaller Spearo may opt for a longer band of greater diameter to make the bands easier to reach. The 3 to 1 ratio we use approximates that of bands specified by most OEM's. We prefer adjusting power by changing the number and diameter of bands while maintaining the 3 to 1 length.

If you would like more technical information on the power of different band diameters, take a look at the Band Power page in the Reference section of our site.