OUTSIDE WRAPS FOR BOXES Wrapping paper equivalent to the strength of the average  grocery  bag  may  be  used  to  wrap  parcels. (Wrapping paper is not required, nor recommended by the  USPS,  if  the  box  itself  is  an  adequate  shipping container.) ENVELOPES Envelopes may be used as containers for articles when they can reasonably be expected to be handled and delivered without damage to the contents or other mail.    Letter-style  envelopes  are  flat  envelopes  that meet the minimum and maximum size requirements. Envelopes  of  this  type  are  not  reinforced  and  are acceptable  as  containers  for  nonrigid  stationery  and material  of  a  similar  nature  that  does  not  exceed  l pound in weight and l inch in thickness.   Envelopes exceeding  the  size  for  letter  style  and  made  from extra-strength materials are acceptable for easy loads up to 5 pounds. FIBERBOARD TUBES AND LONG PACKAGES Fiberboard  tubes  and  similar  long  packages  are acceptable provided their length is not more than l0 times the girth (diameter) of the article. Tubes are ideal for mailing rolled items such as unframed paintings, documents, fishing rods, and so forth.  If the tube is of the two-piece type, where one end slides into the other, tape must be applied to completely encircle the seams where the two pieces are joined. The ends of tubes may be closed by crimping or with tape only if the contents are  rolled  lightweight  items.     Otherwise,  the  ends should be closed with a material as strong as that of which the tube is made. CANS AND DRUMS Cans  and  drums  are  acceptable  if  they  have positive  closures  (the  top  screws  on,  is  secured  by bolts,  clamps,  and  so  forth).     Generally,  friction closures by themselves are not acceptable.   Devices that are closed with locking rings that stick out must be padded to prevent injury to mail-handling personnel, equipment, or other mail.  Cans and drums should not be sacked or pouched regardless of their weight.  They must  be  dispatched  as  outside  mail  (OSM)  to  make sure that equipment or postal personnel are not injured. Q3-1. What are the three types of packaging loads used  in  the  transportation  industry  that  are recognized by the USPS? Q3-2. An   average   load,   as   defined,   weighing   20 pounds   requires   a   fiberboard   box   of   what burst strength? Q3-3. Packages with surfaces that will not retain an adhesive  postage  meter  impression  are  not acceptable for mailing.   (True/False) Q3-4. Paper  wrappers  should  not  be  used  when  a p a rc e l   ( b o x   t y p e )   i s   m a i l e d   i f   w h a t circumstance exists? Q3-5. Fiberboard tubes and similar long packages are   acceptable   for   mailing   provided   their length  does  not  exceed  what  amount  of  the girth (diameter)? Q3-6. What type of closure must a metal can or drum have to be accepted for mailing at a military post office? Now turn to appendix 1 to check your answers. 3-3 Select the Proper Container Strength Certificate Fiberboard containers are generally strong enough to ship material of average weight and size.  These are the common boxes which are readily available in the home, supermarket, hardware store, etc.  An "average" parcel may be defined as one which is no more than 34" X 17" X 15" and weighs 25 pounds or less. with automated parcel processing. Fiberboard strength is indicated on the box, manufacturer’s strength certification printed on the bottom of the box.  This certification is usually a round imprint with four numbers noted. These are the dimensions normally associated PCf0302 Figure 3-2.—Test burst strength shown on a fiberboard box.