The spring you need for your dual blinds is likely a custom or manufacturer-specific part from Redwood, as its 7-inch length on a ¾-inch roller tube does not match any standard Irvine roller shade springs we stock. Because spring length and tension are critical for proper operation, substituting with a standard spring could damage your shade or fabric. We recommend contacting Redwood RV or the original shade manufacturer directly to obtain the correct replacement spring or to inquire about replacing the entire roller assembly. If you have further questions or need additional assistance, feel free to reach out.