HT stamps on it, but my supplier gave me a document that says it was heat-treated. Is that OK? No, each full-sized piece used in the program must have an HT or KDHT mark issued... of it. I build plywood boxes reinforced with solid wood inside, mounted on skids. The skids are hidden under the box, so a stamp mark there is difficult to see. Can I put the marks... sides of the package. Many facilities mark all four sides of a box to insure that the mark is always visible upon inspection. It is also wise to mark the skids as well...