The McCormick TL3660101M91 is an authentic OEM spring designed for various McCormick X-series tractors, including X4.20, X4.30, X4.40, X4.50, X4.60, X4.70, X5.20, X5.30, X5.40, X5.50, X5.60, X6.420, X6.430, X6.440, X7.440, X7.450, X7.460, X7.650, X7.660, X7.670, X7.680, X8.660, X8.670, and X8.680 models. This genuine replacement part also fits a wide range of Landini and ARGO TRACTORS models, ensuring proper function and reliable fitment in compatible agricultural machinery.