「Zにおけるねじ山は、 一定のリード角を有するように形成される遊び側フランクと、 リード角がゼロであるAとリード角が急な区間であるBとが交代して交互に連続するようにステップ状に形成される圧力側フランクと、を有するように形成されている。」という一文を英訳するなら、

The thread of Z is constructed to include a play side flank formed having a specified lead angle, and a pressure side flank formed into a step-like configuration, in which a flat portion whose lead angle is 0 and an inclined portion whose lead angle is steep are continuous alternately.

よりも、

The thread of Z is constructed so as to include a play side flank that is formed with a lead angle of a predetermined degree and a pressure side flank that is formed into a step-like configuration, in which a flat portion whose lead angle is zero and an inclined portion whose lead angle is steep alternate continuously.

の方が正確です。最初の訳文の「are continuous alternately」という表現は、表現自体が矛盾していて理解不能です。