Most corrugated boxes have either a round or square manufacturer's certification stamp (or cert stamps for short) printed on them. However, it is not required for all boxes. Boxes that are not shipped on common carriers or are used only as inner packs do not need cert stamps. Moreover, common carriers may, at their own discretion, choose to ship boxes without stamps. However, they may deny damage claims and/or charge higher freight rates than usual to ship products in uncertified boxes.
The use of the usual round certification stamp on any box indicates that the box has been manufactured in accordance with either the rail or motor carriers classifications (i.e. rule 41 or item 222). This constitutes a guarantee by the box maker that may lead to legal liabilities if the box fails due to an error in the stamp. Thus, it is not suggested that round cert stamps be used when the end use of the box is not known to the box maker. In many cases a rectangular form of stamp certifying only the burst strength of the corrugated board may be substituted for the round stamp providing this is sufficient for the customer's needs.
There is a provision in both rule 41 and item 222 which permits the use of boxes of greater size than normal certificate limits if the weight of box and contents is correspondingly below normal limits. If this provision is used, it must be so noted in printing below the usual certificate.
For very large or heavy products the provisions of rule 41 or item 222 are so restrictive as to make it impractical or impossible to design an adequate package. When this occurs it is often possible to take advantage of other provisions of the rail and motor carriers classifications which specify "F" (for furniture) packs or "numbered" packs. These specifications describe complete packages including interior pads. When boxes can be designed to comply with either type of provision, numbered packs are generally the better choice. Certificate stamps for numbered packs are also rectangular in form but include the package number in addition to burst strength of the board and the boxmaker's name, etc.