CSA G40.21 is a standard specification published by the CSA (Canadian Standards Association). This standard contains the specification for cold-formed welded and seamless carbon steel structural tubing in round, square, and rectangular shapes. It is commonly specified in Canada for hollow structural sections. CSA G40.21 defines several grades based on chemical composition, mechanical property and charpy test value. MOST typically produces and stocks the 350W grade HSS, but can also produce to the higher strength (480W) and the corrosion resistant "AT" grades.