Yanmar 1GM User Manual page 13

6
Nut s
C HA PTER OI':E
OPENINGS FOR TOOLS
Sioned Ph illips All en Internal torx Extern al torx
cA~~~~
MACHINE SCREWS
Self-Locking f asten ers
Nuts are manufactured in a variety of type s and sizes.
Most are hexagonal (6-sided ) and fit on bolts , screws and
studs with the same diameter and pitch.
f igure 11 shows several types of nuts. The commo n nul
is generally used with a lockwasher. Self-locking nuts
have a nylon insert thai preve nts the nut from loosening;
no lockwas her is req uired. Wing nuts are designed for fast
removal by hand. Wing nuts are used for convenience in
non-criticallocations.
To ind icate the size of a metric nut, manufacturers spec-
ify the diameter of the opening and the thread pitch. This
is simi lar to
bolt
specifications, but without the length di-
mension. The measurem ent across two flats on the nut in-
d icates the wrench size 1 0 be used .
•
Several type s o f bolts, screws and nuts incorporate a
system that develops an interference between the bo lt,
screw, nut or tapped hole threads. Interference is achieve d
in variou s ways: by distort ing threads, coating threads
with dry adhesive or nylon , d istorting the top of an
all- me tal nut, or using a nylon insert in the cen ter or at the
top of a nut.
Self-locking fasteners offer greater holding strength
and better vibration resis tance. Some self-locking fasten-
ers can be
reused if in good co ndition. Others, like the ny-
lon insert nut , fonn an initial locki ng conditio n whe n the
nut is first insta lled - the nylo n forms closely to the bo lt
thread pattern, thus reduci ng any tendency for the nut to
loosen. When the nut is removed, the locking efficiency is
grea tly reduced . It is reco mmended tha i new self-locking
fastene rs be installed after they are removed.