A nut is a type of fastener with a threaded hole. Nuts are almost always used opposite
a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination
of their threads' friction, a slight stretch of the bolt, and compression of the parts.
In applications where vibration or rotation may work a nut loose, various locking mechanisms
may be employed: Adhesives, safety pins or lockwire, nylon inserts, or slightly oval-shaped
threads. The most common shape is hexagonal, for similar reasons as the bolt head - 6 sides
give a good granularity of angles for a tool to approach from, but more corners would be
vulnerable to being rounded off. Other specialized shapes exist for certain needs, such as wing
nuts for finger adjustment and captive nuts for inaccessible areas.
Nuts are graded with strength ratings compatible with their respective bolts; for example,
an ISO property class 10 nut will be able to support the bolt proof strength load of
an ISO property class 10.9 bolt without stripping. Likewise, an SAE class 5 nut can support the
proof load of an SAE class 5 bolt, and so on.
A wide variety of nuts exists, from household hardware versions to specialized industry-specific
designs that are engineered to meet various technical standards.
Types
Acorn nut Barrel nut
Cage nut Clip-on nut
Coupling nut Cross dowel
Flange nut Insert nut
Sex bolt Slotted nut
Split nut Sleeve nut
Square nut Staked/welded nut
Swage nut T-nut
T-slot nut nut Weld nut
Well nut Wing nut
Locknuts
Castellated nut Distorted thread locknut
Centerlock nut Elliptical offset locknut
Toplock nut
Interfering thread nut Tapered thread nut
Jam nut Jet nut
Keps nut with a star-type lock washer Nyloc plate nut
Polymer insert nut Serrated face nut
Serrated flange nut Speed nut
Split beam nut Standard metric hex nuts sizes
Note that flat sizes differ from industry standards. For example, wrench sizes of fastener
used in Japanese built cars comply with JIS automotive standard.
Standard SAE hex nuts sizes Classifications
Manufacture
Use of two nuts to prevent self-loosening In normal use, a nut-and-bolt joint holds
together because the bolt is under a constant tensile stress called the preload. The preload
pulls the nut threads against the bolt threads, and the nut face against the bearing surface,
with a constant force, so that the nut cannot rotate without overcoming the friction between
these surfaces. If the joint is subjected to vibration, however, the preload increases
and decreases with each cycle of movement. If the minimum preload during the vibration
cycle is not enough to hold the nut firmly in contact with the bolt and the bearing surface,
then the nut is likely to become loose. Specialized locking nuts exist to prevent
this problem, but sometimes it is sufficient to add a second nut. For this technique to
be reliable, each nut must be tightened to the correct torque. The inner nut is tightened
to about a quarter to a half of the torque of the outer nut. It is then held in place
by a wrench while the outer nut is tightened on top using the full torque. This arrangement
causes the two nuts to push on each other, creating a tensile stress in the short section
of the bolt that lies between them. Even when the main joint is vibrated, the stress between
the two nuts remains constant, thus holding the nut threads in constant contact with the
bolt threads and preventing self-loosening. When the joint is assembled correctly, the
outer nut bears the full tension of the joint. The inner nut functions merely to add a small
additional force to the outer nut and does not need to be as strong, so a thin nut can
be used. See also
References
Bibliography Bickford, John H.; Nassar, Sayed, Handbook
of bolts and bolted joints, CRC Press, ISBN 978-0-8247-9977-9 . External links
Boltdepot.com