The accuracy of manufacturing lead screws of a trapezoidal profile functionally depends on the accuracy of the thread tool and on the value of its geometric parameter - the rake angle, on which the productivity of the thread turning process largely depends. Analytical dependencies are proposed for predicting the accuracy of the trapezoidal profile of the thread made by a turning tool. A computer program has been developed on their basis, which allows, based on the input standard data on the major diameter and thread pitch, to obtain the calculation of the half-profile angle and its deviations along the flank surface, which, as proven, is a curved line. However, its curvature is critically small and can be neglected. The presented example indicates that when using a cutting tool with a -5° rake angle to turn a lead trapezoidal thread screw with a major diameter of 22 mm and a pitch of 8 mm, the deviation of the half-profile angle reaches 0.18°, which is half the tolerance.