Joining of the parts of clothing items in the clothing industry is mostly done with sewing threads, of which polyester threads occupy a significant place. At the joining places e.g sewing, together with the seams and stitches, the threads should provide adequate comfort to the garment. The characteristics of the seams will also depend on their characteristics. The paper analyzes polyester threads from staple fibers, linear density from 23 tex to 48 tex. The dependences between the mechanical characteristics of the threads and the threads in the loop, as well as their mutual relations by the corresponding coefficients are presented. The obtained results can be used by manufacturers of sewing threads and clothes in the design and the selection of threads for the purpose of predicting the mechanical characteristics of seams on garments.