Product Info Catalog Hardware Builders Hardware Springs Extension Spring, 1-In. OD x 12-In. Extension Spring, 1-In. OD x 12-In. Request a Quote UPC: 38594003039 SKU: 681676 Model Number: C-303 1" OD, Extension Spring, 12" Length, .105" Wire Diameter, 11.7" Maximum Deflection, 35.4 LB Maximum Safe Load, Bulk With UPC.