The following SAE Recommended Practice furnishes sample forms for helical compression, extension and torsion springs to provide a uniform method for specifying design information. It is not necessary to fill in all the data, but sufficient information must be supplied to fully describe the part and to satisfy the requirements of its application. For detailed information, see âDesign and Application of Helical and Spiral Springs - SAE HS 795â, also âHelical Compression and Extension Spring Terminology - SAE J1121â. Both of these documents use SI (metric) Units in accordance with the provisions of SAE TSB 003, as does SAE J1122. Here, however, the U.S. Customary Units (in, lb, psi) have been added in parentheses after each SI Unit for the convenience of the user who must furnish specifications on a project where all requirements are listed in non-metric terms.