In fatigue study of thread connection, it is general that the thread connection is replaced by single thread. So, it's very important to study fatigue equivalence of single thread and thread connection. A finite element method (FEM) model is developed to compute strain state of single thread and thread connection. An analysis of fatigue equivalence of single thread and thread connection with the fatigue parameter of strain and obtain the relation between fatigue life of single thread are obtained by fatigue...