Jam Nut
   HOME

TheInfoList



OR:

A jam nut is a low profile type of nut, typically half as tall as a standard nut. It is commonly used as a type of
locknut A locknut, also known as a lock nut, locking nut, self-locking nut, prevailing torque nut,. stiff nut or elastic stop nut, is a Nut (hardware), nut that resists loosening under vibrations and torque. Prevailing torque nuts have some portion of ...
, where it is "jammed" up against a standard nut to lock the two in place. It is also used in situations where a standard nut would not fit. The term "jam nut" can also refer to any nut that is used in the same function (even a standard nut used for the jamming purpose). Jam nuts, other types of
locknut A locknut, also known as a lock nut, locking nut, self-locking nut, prevailing torque nut,. stiff nut or elastic stop nut, is a Nut (hardware), nut that resists loosening under vibrations and torque. Prevailing torque nuts have some portion of ...
s, lock washers, and thread-locking fluid are ways to prevent vibration from loosening a
bolted joint A bolted joint is one of the most common elements in construction and machine design. It consists of a male threaded fastener (e. g., a Bolt (fastener), bolt) that captures and joins other parts, secured with a matching female screw thread. Ther ...
.


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 In continuum mechanics, stress is a physical quantity that describes forces present during deformation. For example, an object being pulled apart, such as a stretched elastic band, is subject to ''tensile'' stress and may undergo elongati ...
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 In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...
, so that the nut cannot rotate without overcoming the
friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Types of friction include dry, fluid, lubricated, skin, and internal -- an incomplete list. The study of t ...
between these surfaces. If the joint is subjected to
vibration Vibration () is a mechanical phenomenon whereby oscillations occur about an equilibrium point. Vibration may be deterministic if the oscillations can be characterised precisely (e.g. the periodic motion of a pendulum), or random if the os ...
, 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 In physics and mechanics, torque is the rotational analogue of linear force. It is also referred to as the moment of force (also abbreviated to moment). The symbol for torque is typically \boldsymbol\tau, the lowercase Greek letter ''tau''. Wh ...
. 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 A wrench or spanner is a tool used to provide grip and mechanical advantage in applying torque to turn objects—usually rotary fasteners, such as nuts and bolts—or keep them from turning. In the UK, Ireland, Australia, and New Zealand ...
while the outer nut is tightened on top using the full torque. This arrangement causes the two nuts to push against 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. The jam nut essentially acts as the "other object", as the two nuts are tightened against each other. They can also be used to secure an item on a fastener without applying force to that object. This is achieved by first tightening one of the nuts onto the item. Then the other nut is screwed down on top of the first nut. The inner nut is then slackened back and tightened against the outer nut. Jam nuts can also be used in situations where a threaded rod must be rotated. Since threaded rods have no bolt heads, it is difficult or impossible to apply torque to a threaded rod. A pair of jam nuts is used to create a point where a wrench may be used. Jam nuts can be unreliable under significant loads. If the inner nut is
torque In physics and mechanics, torque is the rotational analogue of linear force. It is also referred to as the moment of force (also abbreviated to moment). The symbol for torque is typically \boldsymbol\tau, the lowercase Greek letter ''tau''. Wh ...
d more than the outer nut, the outer nut may yield. If the outer nut is torqued more than the inner nut, the inner nut may loosen up.


References

Nuts (hardware) Kontermutter {{Mech-engineering-stub