Here's a quick excerpt:
...and from there it goes into more technical details. Hope this helps make that hardware grade choice a better one.Bolt Grades
I have been on a quite a few online email lists over the last 7 years or so, basically since they first came
out. From the original Jeep-L list to the XJ-list to the Rockcrawler.com board, a common question comes
up time and time again. No, I’m not talking about “how big a tire can I fit” or “which tire is better.
” I’ll save those questions for the opinion section of everyone elses website. I’m referring to the age-old quest
ion of “which fastener grade should I use?”
It seems that everyone has an opinion on which grade is better but not many people can or will tell you
why. Well, I’d like to explain the technical difference between a SAE Grade 8 (Grade 8) and a SAE Grad
e5 (Grade 5) fastener.
Most people think a bolt is a bolt is a bolt. They see it as a machined chunk of metal that holds or
attaches things. Fasteners (aka bolts or screws) are complex mechanically-engineered hardware. They
are made using different materials, different thread types (i.e. coarse, fine, extra fine), various lengths,
with grip or no grip (shank), different types (i.e. hex, 12 pt, carriage, etc.), different coatings (i.e.
passivated, cadmium, dry film lube, etc.), various classes of fit (i.e. class 3), and multiple grades (i.e.grade 5, 8, etc.).
Bolts come with left or right hand threads, metric or SAE threads, different number of threads per inc
h (i.e.20 or 28 for the same size fastener) and various versions of those (i.e. UNF versus UNJF). In addition,
there are way too many military specs in existence to list them all here. So with all these differences,
it’s no wonder most people don’t understand the difference between fasteners very well. Of all these
differences, I’ll focus on the different grades since that is what most shade tree mechanics ask about.
First, you need to be able to identify bolts by the different grades when you go to the local hardware store.
Grade 5 bolts have 3 marks or lines on the head that are in the shape of a “Y”. Grade 8 bolts have 6 marks
on the head.
Second, the different grades have a meaning to them. It tells you how strong the fastener is. There are
different types of strengths listed for each grade. Proof strength (about 90% of yield), ultimate tensile
strength (bolt fails in stretch), yield strength (bolt begins to get a permanent set and changes cross-sectional
area typically) and shear strength (bolt prevents parts from separating by using it’s shank or body as a stop).
Depending on how you are using the fastener, you would look at the appropriate and corresponding strength type.
For example, bolts that attach a D-ring bracket to the bumper face of a vehicle would be critical
in tension . So you would want to know what the tensile strength a particular bolt is.
Bolts that attach winch-mounting plates are typically seeing mostly shear loads thus preventing the winch
from departing from the vehicle during winching operations. In that case, shear
strength is important to you.
It's question that comes up frequently when adding "stuff" as it were to our rigs.
Mark