Iso Metric Screw Threads; Machine Screws; Nuts - Polaris 1999 Sportsman 400 Service Manual

GENERAL INFO RMATION
Grade mar king
The best way to te ll if two fast ener s' threads
match is to turn the nut on the bolt (or the bo lt into
the threaded hole in a piece of equipme nt) with fin-
gers onl y.
Be
sure both pieces are clean. If ex cessive
force is required, check the thread condition on each
fastener. If the thread condi tion is good but the fas-
tene rs jam, the thread s are not compatible. A thread
pitch gauge can be used to de termi ne pitch . Polaris
vehicles arc manufactured with ISO (Inte rnational
Organization for Standardization) metric as we ll as
Ame rican fasteners. Th e threads are cu t di fferent ly
than those of American faste ner s. All engi ne fasten-
ers are metr ic threa ds while the frame component s
are secured with America n thread s
Mo st threads are cut so that the fasten er must be
turned clockw ise to tighten it Th ese arc called
right-hand threads. Some fasteners have left-hand
threads; they must be turn
ed co untercloc kw ise to
be
tightened. Left-hand thre ad s are used in locat ions
where normal rotation of the equipment would tend
to loosen a right-hand threaded fastener.
IS O Metric Screw T hre ads
(Bolls, Nu ts and Screws)
ISO (International Organization for Sta nda rdiza-
tion) metri c threads come in three standa rd thread
sizes: coarse, fine and constant pitch. The ISO
coarse pitch is used for almost all common fastener
applications. The fine pitch thread is used on certain
preci sion tools and instrum ents. T he co nstant pitch
thread is used mainly on mac hine parts and not for
faste ners . The constant pitch thread, however, is
used on all metric thread spark plugs.
Met ric screws and bolts are classifie d by len gth
(L, Figure 5), nominal diameter (D ) and distance
between thread crests (T). The numbe rs 8 x
7
1.25-1 30
identifi es a typical bolt . wh ich wou ld in-
dicate tha t the bolt has a nomin al diameter of8 mm,
the distan ce between thread crests is 1.25 111m an d
bolt length is
130
mm .
1I;·IRNING
Do no t install sc reu- ' s or bolts with a
lower strengt h grade classifica tion
than installed originally by the manu-
facturer. Doing so may calise engine
or equ ipment failure and possible in-
j ury.
The mea surem ent acro ss two fl ats on the head of
the bolt indi cates the prop er wrench size to use. Flg-
nrc 4
Sh O\\o'5
how
to
determine bolt diameter. Wh en
buying a boll from a dealer or part s store, it is im-
portant to know how to spec ify bolt length . Th e cor-
rect way
1 0
measur e bolt length is by measuring the
len gth starting from undernea th the bolt head to the
end of the bolt. Always measure bolt length in this
mann er to avoi d buy ing bolt s that are of the wrong
length.
Machine Screws
There are man y different types of machin e
screws . Th e screw head s arc also designed to pro -
trud e above the metal (round) or slightly rece ssed in
the me tal (flat) . See Figure 6.
Nuts
Nuts are manu factured in a variety o f type s and
sizes. Most are hexagonal (6-sided) and fit on bo lts,
screws an d studs with the same diamete r and pitch,
Th e common nut is ge nerally used with a
lock washer. Se lf-locking nuts have a nylon insert
tha t prevents the
nu t
fro m loosenin g; no lockwasher
is requi red . Wing nut s are designed for fast removal
by hand . Wing nuts are used for co nvenience in
non -critica l locations.
To
indicate the size of
a
metric nut. man ufac turers
speci fy the d iameter of the ope ning a nd the thread
pitch. Thi s is sim ilar to bolt spec ifications. but with -
ou t the length dimen sion. Th e measu rem ent acro ss
two flats on the nut indicates the proper wrench size
to be used
.