A nail’s holding power is a function of its diameter, how far it penetrates the wood, and the type of wood it penetrates.
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Holding Power of Nails
In framing, nails should never be loaded in withdrawal (where the load acts parallel to the nail shank and tries to pull it out). Instead, framing nails should be loaded laterally (where the load acts perpendicular to the shank). Also, nails have more holding power when driven into the side grain rather than into the end grain. In fact, nailing into the end grain will reduce a nail’s lateral load capacity by approximately one-third.
Box vs. Common Nails
Lateral strength is largely a function of a nail’s diameter and the density of the type of wood into which the nail is driven. For example, 10d and 12d nails have the same diameter and the same lateral strength in each type of wood. Common nails are stronger than box nails because of their greater diameter (below).
When substituting box for common nails, calculate the nail size needed using the conversion ratios shown below.
Figure: Conversion Ratio for Common to Box Nails
S-P-F lumber assumed.
Do not substitute a common nail that’s specified on the plans for an equal number of box nails. Instead, multiply the specified number of common nails by the conversion ratio shown in the chart and round up to find the equivalent number of box nails.
Withdrawal Strength of Nails
Nails are much stronger when loaded laterally (across the nail) than when loaded in withdrawal (along the length of the nail). Withdrawal from end grain is particularly weak and not accepted as a structural connection by most codes. Withdrawal values from sidegrain are given in the table below.
Figure: Withdrawal Strength Design Values in Pounds of Common vs. Box Nails
This table shows the allowable load values for typical common and box nails. These values are in pounds per inch of penetration into the side grain of the main member.
For toenails loaded in withdrawal, multiply the values in the Withdrawal Strength Design Values table, above, by .67. For toenails loaded laterally, multiply the values in the Lateral Strength table, above, by .83. Toenails should be driven at an angle of about 30 degrees from the face of the stud or other member being attached (below).
Figure: Proper Toenailing
psi per inch of penetration into side grain of main member ↩