GENERAL
INF
ORMATI
ON
Bolts
Commonly called bolts, the technical name for
these
fa
steners is cap screws. Metric bolts are de-
sc
ri
bed
by
the diameter and pitch (the distance
between each thread). For example.
an
M8 x 1
.25
bolt is o
ne
that
ha
s a diameter
of8
millimeters a
nd
a distance
of
1.25
millimeters between each thread.
The measurement across
2 flats on the head
of
the
boll indicates the proper wrench size to be used.
Use a
ve
rnier caliper and measure across the
threads (Fig
ur
e 6) to determine the bolt diameter.
Nuts
Nuts are manufactured
in
a variety
of
ty
pe
s and
sizes. Most are hexago
nal
(6-s
id
ed) and
fit
on
boilS,
screws and studs
wi
th
the same diameter and pitch.
Figure
11
shows several types
of
nuts. The
common nut is genera
ll
y used with a lockwasher.
Self-locking nuts have a nylon insert which
@
---
Common nut Self-locking nut
Wing nut
®
..
ACHINE SCREWS
....
Fla •
a.,.
7
prevents the nut from loosening; no lockwasher is
required. Wing nuts arc designed for
fa
st remo
val
by hand. Wing nuts are used for con
ve
nience
in
non-critical loca
ti
on
s.
To indic3le the size
of
a nul. manufacturer
's
spec-
ify the diamet
er
of
the opening and
th
e threads per
in
ch. This is similar to bolt specifica
ti
ons. but
without the length dimensio
n.
The measurement
across
2 flats on the
nut
indicate the proper wrench
size
10 be used. F
igur
e 5 shows how to determine
nut size.
Self·L.ocking Fasteners
Several types of bolts. screws and nuts
incor-
porate a system that develops interference be-
tween the bolt. screw nut
or
tapped hole threads.
Inter
fe
rence is achieved
in
va
rious ways: by di
s·
t
or
ting threads, coating threads with
dr
y
adhe·
sive
or
nylon. distorting the top
of
an all-metal
nut. using
a nyl
on
inse
rt
in the
ce
nter
or
at the top
of
a nut , etc.
Se
lf-locking
fa
stencrs offer greater holding
strength and
be
ner vibra
ti
on resistance. Some
self-locking fasteners can
be
reused
ifin
good con-
ditio
n.
Others, like
th
e nylon insen
nUl.
fo
nn
an
in
i-
tilll
loc
kin
g condit
io
n when
th
e
nu
t is first
in
stalled:
th
e ny
lon
fonus closely to the boh thread pallem.
thus reducing any tendency for the n
ut
10 loosen.
When the nut
is
removed. its locking efficiency
is
greatly reduced. For grea
te
st
safety
il
is
rec
o
m-
mended that new self· locking
fas
ten
ers be installed
whe
ne
ver
th
ey are removed.
Washers
There are 2
ba
sic types
of
wa
shers: flat washers
and lockwashers. Flat washers are
si
mple discs
with a hole to
fit
a screw or boll. Lockwashers arc
Fllli.
ler
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