The T646 portable seam tensile strength tester, manufactured by Zweigle Textilprufmaschinen GmbH, is described. It was developed as a result of research carried out at the Reutlingen School of Technology and Industry by Prof. Dipl.-Ing. Herbert Henne. The research was designed to produce reprducible specifications for minimum seam requirements in knit wear. The construction and operation of the testing device are presented.