Metolius took the same revolutionary shape of the Curve Nuts and applied it to these tiny titans. Metolius chose silicon-bronze because it exhibits the perfect blend of hardness and shear strength. This, combined with a patented Curve Nut shape (modified with a slight transverse taper), gives you micro gear which is easy to visually monitor and sets up the bomber triangulation necessary for a solid placement. The Astro Nuts come in sets designated for aid climbing (sizes 1, 2, 3, 4, & 5) and free climbing (sizes 6, 7, 8, 9, & 10).