Leon wrote:
"J. Clarke" wrote in message
...

It's in "Wood As An Engineering Material", Page 7-11. What they say
is:

"For low-density softwoods, such as the cedars and white pines, 40%
to 70% of the shank diameter; for Douglas-fir and Southern Pine, 60%
to 75%; and for dense hardwoods, such
as oaks, 65% to 85%. The smaller percentage in each range applies to
lag screws of the smaller diameters and the larger percentage to lag
screws of larger diameters."


I wonder if that material was written in modern years or 30 plus. I
see lag screw failures galore.

Are you saying that the properties of wood have changed so radically in the
last 30 years that lag screws hold differently in them now? Because the
recommendations are not about allowing you to use crap screws without
breaking them while driving, they are about sticking wood together so it
stays stuck.