To make your own powerband with ease of assembly , adjustable wishbone length, and easy changeability do the following steps:

• cut to desired length - measure the full distance a fully stretched band would require then subtract 6 (for the wishbone) and divide by 3 to 3.2 depending on how tight you like your bands - that is the length of the powerband rubber. Tighter will mean more power but it will also mean it is more difficult to load. Better to get more power by adding more bands. For high-modulus rubber, you can go up to 3.5 to 1 stretch.
• taper each end - by inserting a nail into the end of the band (wet it first to ease insertion) then using the pedistal grinder taper the end at a 45 degree angle, grinding down until the grinder sparks on the nailhead .
• make the wishbone Sear the ends with a torch or match to prevent fraying.
• tie a figure eight knot in one end of the 10" length of 1/8" nylon paracord. Pull the knot tight with a pair of vice grips.
• construct the bandeye . Here is a shot of the stages of the bandeye assembly. First cut about 6 inches of 400lb mono and thread onto a 2.2 barrel crimp . Then swage the crimp with a large enough loop for the cord to run through. Next install a barrel shot on one leg and a trailing barrel crimp. Swage the entire assembly and then cut the trailing mono to result in the final bandeye
• insert the wishbone end into the powerband end - this is the part I find most difficult, so I use a tool we make to insert them. Put the figure eight into the tool, clamp the tool into a vice and push it on. If you are putting on the double knotted wishbones (we don't - but here is how) reverse the tool here is another shot of it . Silicone spray on the knot and silicone spray up the hole in the rubber will aid in inserting the knot. Wrap cloth around the rubber to protect your hand and then push the rubber over the tool holding the knot. Be sure it is deep enough to allow you to tie a knot over the cord in the next step.
• insert the bandeye using needlenose plyers and silicone spray until its all the way in.
• tie the Constrictor Knot or the Double Constrictor Knot over each end Using plyers pull the knot - be sure it is very tight - so tight that the rubber seems like it is going to burst tie it twice using square knots after the constrictor. Also be sure you tied it as close to the taper as you can but still over the wishbone line. Cut and sear the tag ends of the knot line. I use the waxed wipping line sailors (available at West Marine or better Marine supply stores). Cut about a 12 inch segement when tripled tie figure eights in the waxed line. installation on the gun is easy - thread thru the guns band slot . Then tie a figure 8 in the wishbone cord. The finished product
• test for strength - pull each end apart to be sure the wishbone knot isn't going to pull out. Repeat test on a speargun to be sure it holds. If it pulls out, your constrictor know wasn't tight enough or your figure eight knot was too small.