In this article some expressions of the tensile strain arising at the most frequently cases to the so-called float stitch, in both plain or rib fabrics are worked out. On the basis of the fundamental notions of the theory of elasticity, the possible changes occurring in the knitting thread under the effect of increasing tensile force are clarified. A method is proposed for objective assessment of these changes in order to prevent the breaking of the thread in the knitting process. The observations are made, taking in account the elasticity of elongation only. In the received formula the tensile forces have sense in the value of maximal forces, received in the process of knitting.