To select the correct replacement springs for your RV roller shades, first measure the length of the spring shaft from left to right, which you indicated is approximately 15 inches. Confirm the inside diameter of the end caps, which in your case is 0.75 inches. Based on these measurements, you will need replacement springs with a 0.75" inside diameter. For your convenience, you can order the appropriate 0.75" Irvine replacement springs designed for Valu-Line RV roller shades on our website. If you have an incorrect 1" spring, please use the provided return label to send it back. Proper measurement ensures compatibility and smooth operation of your roller shades.