2632 Chapter 22 



PALLET FASTENERS 



Some plywood-decked pallets are assembled with bolts, and — on an experi- 

 mental basis — some have been assembled with adhesives (Kurtenacker 1969, 

 1973ab, 1975a; R. K. Stern 1975). Bolted assembly is expensive, and because 

 bolts are inserted in oversize holes, pallets so assembled lack rigidity. Adhesive- 

 bonded pallets have generally not withstood the impact loads to which pallets are 

 subjected; also, joints bonded in green wood weaken as boards dry and shrink. 

 The preponderance of pallets are therefore assembled with nails and staples. 

 These nails and staples account for 3 to 6 percent of the total cost of pallets (Bond 

 and Sendak 1970). 



Nail styles. — In stringer-type warehouse pallets, 6-inch deckboards are gen- 

 erally secured with three nails and 4-inch with two (fig. 22-31). In block-type 

 pallets, four nails usually fasten 6-inch deckboards to the corner blocks (fig. 22- 

 29). For normal pallet assembly with pine-site hardwoods in green condition, 

 predrilling prior to nailing is not necessary. W'th very dense woods such as 

 hickory, however, it is often advantageous to predrill the deckboards prior to 

 assembly; predrilling with jigs results in optimum nail location, straight nailing, 

 and fewer split deckboards and stringers (Stern and Franco 1979). 



Both stiff-stock and hardened-steel pallet nails have been used since 1960 for 

 assembly of warehouse pallets; experts are not unanimous in defining these 

 terms, but industry generally accepts the following: 



• Stiff-stock nails are bright, nonhardened, low to medium-high carbon- 

 steel nails. 



• Hardened-steel nails are made of medium- or medium-high-carbon 

 steel, heat-treated and subsequently tempered. Heat treatment and tem- 

 pering makes the nails tough as well as stiff. 



To segregate types of nails, test criteria have been established based on data 

 obtained from a Morgan impact bend angle tester (MIBANT tester). Bend 

 angles on stiff-stock nails may vary from 25 to 60° or more. Hardened steel nails 

 usually have bend angles of 20° or less. Pallet manufacturers normally specify 

 the MIBANT bend angle of nails they purchase. From a 25-nail sample so 

 tested, none should show partial or complete head failure and not more than two 

 should show partial or complete shank failure (E. G. Stem 1974b). 



From field observations during the years 1966 through 1971 of commercial 

 shipping operations at 17 locations in the United States, W. B. Wallin and W. H. 

 Sardo, Jr. concluded that pallet life could be signficantly increased and cost 

 reduced by using hardened-steel nails. E. G. Stern (1974c) confirmed these 

 findings in the laboratory; hardened-steel nails increased rigidity of stringer-type 

 red oak warehouse pallets 64 percent compared with stiff-stock nails of the same 

 size. 



E. G. Stern (1974d) found that for optimum results these hardened pallet nails 

 should be 3 inches long (rather than 2-'/4 or 1-Vi inches), made from 0. 120-inch 

 wire, have four helical flutes with about 60° thread angle and 0. 136-inch thread- 

 crest diameter, be pointless, and have a flattened, thin-rimmed, umbrella head 

 about 5/16-inch in diameter (fig. 22-36). 



