The McCormick 6613921A1 is a genuine OEM engine block designed for a wide range of McCormick X-series tractors. This critical component ensures the structural integrity and proper functioning of the engine, providing a reliable foundation for engine rebuilds or replacements. It is compatible with McCormick X4.30, X4.40, X4.50, X5.35, X5.45, X5.55, X6.420, X6.430, X6.440, X7.440, X7.450, X7.460, X7.650, X7.660, X7.670, X8.660, X8.670, and X8.680 models.