WINTER 2017

104
THE DISTRIBUTOR’S LINK
GUY AVELLON WHAT FASTENER DISTRIBUTORS NEED TO KNOW TO ANSWER CUSTOMER QUESTIONS - PART 3 from page 26
My equipment did not come with a lock
washer; can I add one to the connection?
ANSWER: No.
A good rule of thumb to follow is: if it did not come
with a specific component part, do not add anything other
than OE parts to the connection.
This is not to say that lock washers do not have
their part in maintenance, however, we must go back
to ‘liability’. Again, the dynamics of the connection may
be changed from the addition of something which was
not originally specified. The SAE has basically taken lock
washers out of their Book of Standards over 30 years ago.
In automotive, heavy machinery and off road
equipment, there are no lock washers ever used with
Grade 8 or 10.9 fasteners. Instead, through hardened flat
washers are used. These flat washers must be replaced
with the same type.
Do I need to use a flat washer?
ANSWER: Yes and No.
Here again, it depends upon the application. Most
answers are generic, while others depend greatly upon the
joint materials and application:
Structural steels: While the ASTM A325 and A490
structural bolts have wider heads, the A325 is frequently
used without a flat washer. However, due to the increased
loads produced by the A490 bolts, these joint applications
will usually require an F436 hardened flat washer.
Regular steels: Flat washers should be used
to prevent embedment of the nut or bolt head into a
softer joint material. Flat washers are also used to
protect the surface of the clamped materials and will
provide consistent clamp loading with properly tightened
fasteners.
Soft materials: A large diameter USS flat washer is
used to primarily increase the load bearing surface area
and prevent cracking and embedment.
Since the large diameter USS flat washer
increases the load bearing area, should I only
stock the USS flat washers?
ANSWER: No.
The large diameter USS flat washers will only
increase the load bearing surface area on softer and
thinner materials; sheet metal, fiber glass, plastics,
wood, etc. A large diameter USS flat washer will not
provide any benefit against harder and thicker steels.
The smaller diameter SAE flat washer should be
used on all other surfaces and materials. The only
product that will increase the load bearing surface area
is a flanged nut or flanged bolt head. Here, the washer
is an integral part of the fastener and distributes the
stresses to the outer part of the flange. Normally, the
stresses are axial, generated from the edge of the nut
corners and edge of the hex head of the bolt.
Do flat washers come in different grades?
ANSWER: Yes.
We do not necessarily call them ‘grades’, they are
classified as being either ‘plain’ or ‘through hardened’.
Plain flat washers are made from stamped, low
carbon steel. They are basically soft. If at any time a
fastener was removed where a plain flat washer was
used under the bolt head and / or nut and the impression
of the nut or bolt head was left in the flat washer, at least
one fastener strength level was lost. A fastener will
lose approximately 30,000 psi for each 0.001” of joint
relaxation per inch of effective bolt length. This can lead
to a loose connection or metal fatigue on a heat treated
bolt.
The plain flat washers are effective for the softer
materials. They should never be used with Grade 5 or
Grade 8 or Metric Property Class 8.8 or 10.9 fasteners.
Instead, these higher strength fasteners should be
mated with the through hardened SAE style flat washers.
Unfortunately, most flat washers are not marked.
Several private label distributors will have their hardened
flat washers identified as well as the ASTM F436
structural washers are also predominately marked. Many
distributors will also label their packaging to identify the
washer type, so it is incumbent upon the buyer to know
the difference and use them properly.
GUY AVELLON