[ILDiver]

You'll need inside and outside diameters. The good shops will help you with recommendations if your not sure.

If I was reworking your spear there, I would remove those steel crimps holding the cord into the tubing and tie the new rubber onto that cord. The constrictor knots I mentioned would act like those steel crimps.

If you cut the your current band (don't do it, this is an example) you would have the first part of what I was talking about, right before you tie the overhand knots in the bands.