On the outside of one of the bottom flaps will appear a label called the Box Maker's Certificate. This mark is the maker's certification as to the strength of the box and its materials. Comparing these numbers helps you pick the approriate box for the specific job. Below is a sample certificate for a simple carton.
Burst Test - The force required to rupture the board using vacuum pressure. This relates to the box's ability to withstand forces, and therefore to contain and protect the contents during rough handling.
Combined Weight on Facings - This is a measure of the weight the side of the box can withstand when something is placed on top of the box. This relates to the stackability of the box.
Size Limit - This is the maximum length in inches that a sheet of this board can be while still maintaining its srtength characteristics.
Gross Weight Limit - This is probably the most important measure. This tells us the maximum total weight of contents that can be safely placed in the box.
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