TECHNICAL NOTE number 236 
 
 UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE 
 
 FOREST PRODUCTS LABORATORY 
 MADISON 5. WISCONSIN REVISED \TJ&P^m£_erl 9 5 8 
 
 NAIL-WITHDRAWAL RESISTANCE OI» AMERICAN 'WOODS 
 
 Resistance of a nail to direct withdrawal from a pTe^e-©£^6oti Q$$ffljim{ 
 related to the density or specific gravity of the wood, the diameter -oX the 
 nail, and the depth it has penetrated. The surface condition of the nail 
 and the type of shank and point it has will also influence the withdrawal 
 resistance. 
 
 For bright common wire nails driven into the side grain of wood, the 
 withdrawal resistance immediately after the nail is driven is given by 
 the formula, p = 6900 G~* ' D, in which p represents the ultimate load per 
 lineal inch of penetration in the member holding the nail point; G the 
 specific gravity of the wood based on weight and volume when ovendry; 
 and D the diameter of the nail in inches. 
 
 Relationships expressed by this equation are general and provide informa- 
 tion on the relative withdrawal resistance of different species of wood. 
 Certain species of wood, however, give test values that are somewhat 
 higher or lower than the equation values. Usually common knowledge of 
 the characteristics of the nail, and of the species with particular refer- 
 ence to tendency to split, will aid in deciding whether the withdrawal re- 
 sistance will fall above or below the equation values. 
 
 The general equation indicates that the dense, heavy woods offer greater 
 nail-withdrawal resistance than the ones of lighter weight. This does not 
 mean that the lighter species are not qualified for uses requiring high 
 withdrawal resistance. As a rule, the lighter species do not split as 
 readily as the dense ones; thus lighter woods offer an opportunity for in- 
 creasing the diameter, length, and number of the nails to compensate 
 for the wood's lower nail-holding properties. 
 
 In practically all species, nails driven into green wood and pulled before 
 any seasoning takes place will offer about the same withdrawal resist- 
 ance as nails driven into seasoned wood and pulled soon after driving. 
 However, if common smooth-shank nails are driven into green wood that 
 is allowed to season or into seasoned wood that is subjected to cycles of 
 wetting and drying before the nails are pulled, they lose a major part of 
 their withdrawal resistance. In seasoned wood that is subjected only to 
 
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Nail diameter varies for different types of nails. Here are diameters 
 of bright common wire nails: 
 
 Penny 
 
 Gage 
 
 Diameter 
 
 Penny 
 
 Gage 
 
 Diameter 
 
 4 
 
 12-1/2 
 
 0.098 
 
 12 
 
 9 
 
 0.148 
 
 6 
 
 11-1/2 
 
 .113 
 
 16 
 
 8 
 
 .162 
 
 8 
 
 10-1/4 
 
 .131 
 
 20 
 
 6 
 
 .192 
 
 10 
 
 9 
 
 .148 
 
 
 
 
 034 
 
 0.38 
 
 042 
 
 046 
 
 0.50 054 0.58 
 
 SPECIFIC 0RA\ 
 
 0.70 
 
 Figure 1. --Load required to withdraw common nails from wood of dif- 
 ferent specific gravities immediately after nails were driven. Specific 
 gravity is based on weight and volume of ovendry wood. 
 
 -3- 
 
UNIVERSITY OF FLORIDA 
 
 ii i inn urn im 
 
 3 1262 09216 7922 
 
 moisture changes from normal atmospheric variations, the withdrawal 
 resistance of smooth-shank nails also diminishes in time. On the other 
 hand, tests indicate that, when moisture conditions cause nails to rust, 
 withdrawal resistance is verv erratic; it may be regained or even in- 
 creased over the immediate withdrawal resistance. Under all conditions 
 of use, the withdrawal resistance of nails varies so widely that it is dif- 
 ficult to evaluate their behavior. The withdrawal loads for plain nails 
 driven into wood that is subjected to wide alternating changes in mois- 
 ture content may be as much as 7 5 percent below the values given by the 
 general formula. 
 
 The specific gravity of various species of wood and their relative re- 
 sistance to the withdrawal of smooth- shank nails are given in table 1. 
 There the numerical value of 6900 G^ ' ^ has been calculated for each 
 species. The load per inch of penetration immediately after driving may 
 be obtained by multiplying this nail -withdrawal factor by the diameter, 
 D. For example, table 1 shows a value of 790 D for an eightpenny com- 
 monnail (0. 13 1 -inch diameter) in ponderosa pine. Multiplying 790 times 
 0.131 gives a value of 103 pounds per inch of penetration. 
 
 The curves in figure 1 show the relationship between load for common 
 wire nails and the specific gravity of the wood. By using the specific 
 gravity from table 1, the withdrawal resistance of a given size nail may 
 be obtained directly from the curves. For example, to obtain the with- 
 drawal resistance of an eightpenny (0.131 -inch diameter) common nail 
 in ponderosa pine, follow the specific gravity line at 0.42 upward to the 
 8 D curve. A horizontal line from that point of intersection to the load 
 scale shows a load of 103 pounds. 
 
 The values given herein are for nails driven perpendicular to the grain 
 of the wood. When the nail is driven parallel to the wood fibers -- into 
 the end of the piece -- withdrawal resistance in the softer woods drops 
 to 75 or even 50 percent of the resistance obtained when the nail is driven 
 perpendicular to the grain. The direction at which the nail is driven has 
 less effect on the withdrawal resistance in dense woods than in softer 
 woods. Slant driving of nails is usually superior to straight driving. 
 
 Many other types of nails have been developed for ordinary or special 
 uses. These include annular grooved, spirally grooved, and coated or 
 etched nails. In general, they have been developed to provide higher re- 
 sistance to withdrawal than furnished by the common nail. Under con- 
 ditions involving changes in the moisture content of the wood, annular 
 grooved and spirally grooved nails provide considerably greater with- 
 drawal resistance than the common wire nail. This is especially true 
 of nails driven into green wood that subsequently seasons. 
 
 4-