Radial shaft seals are vital to the performance and longevity of rotating machinery, ensuring effective sealing between moving components. This comprehensive guide explores the key design principles—tolerances, surface finishes, fits, and standards—that govern successful seal performance. By aligning with ISO 286, DIN 3760, and related norms, engineers can enhance durability, prevent leakage, and ensure precision in both low- and high-speed applications. As machinery becomes more advanced, mastering radial shaft seal design will remain essential for achieving operational reliability and extended service life.