Metolius added a transverse taper and silicon-bronze to the revolutionary Curve Nut shape to give these mini-nuts tenacious bite in each and every placement. The finest materials, combined with their patented shape, give you a powerful tool for protecting micro-sized fissures. They looked at many different alloys before settling upon silicon-bronze. Steel was just too hard for micro nuts and didn’t allow them to seat into placements, while aluminum was too soft and didn’t provide enough structural strength. Silicon bronze is the perfect material (although very costly) as it exhibits high strength, yet is still soft enough to let the nut bite into the rock’s surface and seat into position with maximum holding power. Additionally, on their larger sizes, they are able to introduce curves into the faces of the Astro Nuts, giving them a massive placement advantage over regular, straight-sided pieces. The small collars on Curve Nuts are color-coded for quick identification. Astro Nuts are a huge addition to anyone's rack, aid climbers, free climbers and alpinists alike.