Jim Macklin wrote:
Understand that bolts used in aircraft construction are not
"hardware store" items. The steel and the tolerances for
aircraft grade fasteners are better than hardware store
Grade 8 bolts. Beech uses bolts in tension to hold the wing
on the Bonanza, Baron and King Air models. When there is a
crash, the bolts are rarely broken. But if the bolts are
not properly installed and maintained, corrosion can weaken
the bolts causing them to break.

Cessna uses a bolt installed in shear through fittings like
you fingers meshed. This is called "double shear" and as
long as the bolt is a snug fit in the hole the bolt can hold
more load than the airplane is designed to experience.
But a bolt in tension is stronger than a bolt in shear.


The hardware-store Grade 2 bolts (no marks on the head) is
around 55 to 60 ksi, really dangerous stuff on anything other than your
kid's push kart. Grade 5 (three radial marks on the head) are 120ksi,
same as an AN bolt. The Grade 8 (five radial marks) is 150ksi, better
than the AN bolt.
But the AN bolt is made of 2330 nickel steel, making it more
corrosion-resistant and more ductile, which means it will stretch more
before it breaks. The part will appear loose before it comes off. The
AN bolt's tolerances are a bit better and the thread length is just
what's needed, not the great length of thread on the industrial bolt
that ends up inside the joint where it doesn't support the shear loads
well. And the thread fit is far better on the AN bolt.
Shear strength for steel is typically 70% of tensile.

Someone asked about the Cardinal's (177) wing attach. It's been a
long time, but I think it was something like 1/2" bolts in sextuple
shear, spaced about 7 inches apart. The spar fittings were cast
aluminum.

Dan