Staples and steel stitching are acceptable for closing a mailing container if
they are spaced for the load type as follows:
• For an easy load or an average load, not more than 5 inches apart.
• For a difficult load, not more than 2-1/2 inches apart.
Staples must not be more than 1-1/4 inches from the ends of the box or
mailing container. If a box's staple spacing does not meet these
requirements, the box should be banded to compensate for the gap in the
staple closure, or a strip of 3-inch-wide reinforced tape should be applied to
the box between the staples (as shown in the illustration).
Envelopes, flat-size mailing containers, or cards that have partially opened
staples are not acceptable for mailing.