Primeline's industry-leading 16mm speargun rubber offers the highest quality latex, sold in 10cm increments. Manufactured in Primeline Industries, which provides fast and fresh rubber through their large volume. Sealed opaque plastic packaging protects the rubber from ozone and UV rays. For Primeline rubber, a 310% stretch is recommended. To determine band length, measure muzzle-shark fin then multiply by 2, subtract 4", and divide by 3.1 (310% stretch). For more power, increase stretch to 350%, but it can be difficult to load short bands from Primeline rubber.