The broken plastic part inside the roller tube of your Forest River Sabre's shade is part of the spring assembly, which is manufactured as a single unit and not sold as individual internal components. Since your roller shade matches the Irvine 3/4" x 24" Valu-Line model, you can replace the entire spring assembly with the Irvine Replacement Spring 3/4" x 24" available at Elkhart RV Parts. This ensures proper fit and functionality. If your shade turns out not to be an Irvine product, the specifications may differ, and you might need to consider ordering a complete custom shade through Elkhart RV Parts' Custom Shade Builder. For more information and to order the replacement spring, visit the Irvine Shade Springs collection on our website or contact our customer care team for assistance.