Mechanical Diode® type one way clutches are positive locking, planar ratchet type one way devices. They are designed for exceptionally high lock up torque along with virtually wear-free overrunning operation. This paper presents a method of predicting Mechanical Diode (MD) ultimate strength. MD strength is dependent upon the reaction element within the clutch called the strut. Lockup forces are supported by the strut. By calculating the column buckling strength of the struts, a predictive measure for determining clutch load carrying capacity is outlined. The method of computing buckling strength is shown and a sample calculation for an MD design is included. Data on overload failure due to strut buckling is presented and compared with the calculated failure torque for a typical MD. The experimental data includes not only the maximum torque at failure, but also provides traces showing the elastic and plastic response regions of the strut in compression. Results of this study indicate that MD ultimate strength is extremely high for the device's weight and volume and that the ultimate strength can be predicted with sufficient accuracy to allow reliable designs.