Stanley extension springs come in three loop types; machine hooks, extended hooks, and cross over hooks. Wire thicknesses range from .012 - .188. Materials include hard drawn wire, music wire: zinc coated music wire, galvanized music wire, tinned music wire, preco-z music wire; stainless steel wire including: annealed stainless steel, 302 – 304 stainless steel, 316 stainless steel, 17/7 stainless steel, elgiloy wire, nichrome wire, nickel coated copper wire, oil tempered wire, galvanized hard drawn wire.