Solid Wood Products 2635 



Staples. — Staples as well as nails are used as pallet fasteners in warehouse 

 and exchange pallets. Steel wire for these staples should be 15 gauge or larger 

 and have a tensile strength of at least 120,000 pounds. The staples should be 

 driven so the crowns make a 45-degree angle with deckboard grain and be 

 countersunk 1/16-inch. Number of staples per joint are specified by pallet 

 purchasers. 



Stem (In press b) further compared the 2-i/2-inch-long, 15-gauge plastic 

 coated staples described in footnote 3 of table 15 with the 3-inch nails described 

 in footnote 2; he concluded that approximately three times as many 2-1/2-inch 

 staples as 3-inch nails may be required to provide equivalent deckboard-stringer 

 separation resistance in hardwoods in the axial direction of the fasteners. To 

 replace 2- !/2-inch-long nails similar to the 3-inch nails, at least twice as many 

 staples as nails may be required for equivalency. These comparisons assume that 

 fasteners do not split deckboards or stringers during assembly. Field perform- 

 ance data for southern hardwood pallets assembled with such large numbers of 

 staples are not available, however. 



Kurtenacker (1973b) found that northern red oak joints of sawn lumber 

 assembled with such staples did not perform as well in static loading of pallet 

 comers as did an equal number of 2-14- or 2- '/2-inch pallet nails; in impact tests, 

 however, comers with the plastic-coated staples performed as well as, or better 

 than, nailed corners. Kurtenacker (1975a) concluded that for fastening northem 

 red oak deckboards of knife-cut, parallel-laminated veneer, such staples per- 

 formed satisfactorily if about five staples were substituted for every three pallet 

 nails. 



Performance of staples in 22 southern hardwoods. — The effectiveness of 

 the l-Vi-'mch staples was evaluated in southern hardwood deckboard-stringer 

 joints by E. G. Stem (1976). Test conditions were the same as those described 

 for table 22-15. Staples in Stem's test had semi-flat legs (0.067 by 0.073 inch), 

 short symmetrical chisel points, and were driven by an air-gun, one per joint. 



Crown pull-through resistance, which averaged 614 pounds (table 22-15) was 

 minimum in yellow-poplar (456 pounds), sweetbay (463 pounds), and sweet- 

 gum (513 pounds); it was maximum in winged elm (81 1 pounds) and red maple 

 (773 pounds). 



Leg withdrawal resistance, which averaged 257 pounds (table 22-15), was 

 minimum in red maple (105 pounds), hackberry (120 pounds), and yellow- 

 poplar (152 pounds); it was maximum in northern red oak (538 pounds), laurel 

 oak (497 pounds), and Shumard oak (494 pounds). Leg withdrawal resistance 

 from mockemut hickory was only 190 pounds, about the same as from sweet- 

 gum (188 pounds). 



For these staples, forces (in pounds) were loosely correlated to wood specific 

 gravity based on ovendry volume and weight (G), as follows: 



Staple-crown pull-through resistance = 1 ,024G (22-3) 



Staple-leg withdrawal resistance = 194G^'^ (22-4) 



