ASTM A500 is a standard specification published by the ASTM for cold-formed welded and seamless carbon steel structural tubing in round, square, and rectangular shapes.
It is commonly specified in the US for hollow structural sections, but the more stringent CSA G40.21 is preferred in Canada.
ASTM A500 defines four grades of carbon steel based primarily on material strength.
[2] A500 cold-formed tubing comes in four grades based on chemical composition, tensile strength, and heat treatment.
The yield strength requirements are higher for square and rectangular than for round tubing.