The resistance of a nail to withdrawal from wood-based materials is characterized by several factors, including framing member material density and moisture content/conditioning, nail shank diameter, and the depth of penetration (US Department of Agriculture [USDA] 2010).
The stronger correlation between density and withdrawal capacity for the annular and helical nails compared with 8d common nails could be due to the capacity of the 8d common nail relying primarily on friction, whereas the withdrawal capacity of the annular and helical nails also depends on the bearing strength of the wood in contact with the nail shank deformations.
The key to TetraGrip(TM) technology is the proprietary nail shank
The shortening of the length of the cantilevered nail, which occurs with the increasing nail-drive depth, causes the bearing area between the nail shank and the sheathing to decrease.
Based on nail shank diameter, joints flush driven with common nails should be approximately 80 percent stiffer than joints flush driven with cooler nails, all other factors being equal.
The cooler nail shank within the plywood thickness may behave more like a fixed-fixed beam than like a fixed-free (cantilever) beam.
When again exposed to moisture, the wood fibers of the deckboard expand, gripping the nail shank and at the same time, the joist swells in depth, causing the nail to be pulled from the joi st.
Fiber relaxation and changes in moisture content greatly affect withdrawal resistance of nail shanks (FPL 1999).