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Introduction of bolts and nuts

What is a bolt

A bolt is a type of fastener which is used to join two parts together. The bolts join the part non- permanently i.e. the parts may be separated from each other by using an appropriate tool. Nuts are also used on the bolts to make the fastening process more effective. 

The composition of the bolt

A bolt comprises of two parts and these are


(1) Head: The upper portion of the bolt is called ahead. The head may have different shapes. The shape of the head depends upon the purpose for which the bolt is required.


(2)Shank: The cylindrical portion of the bolt is called shank. The tail end of the bolt is threaded to a sufficient length so that a nut can be engaged in it. 

Type of bolt


(1)Anchor bolt 

(2)Carriage bolt 

(3)Elevator bolt 

(4)Flange bolt 

(5)Hanger bolt 

(6)Hexagon bolt/Tap bolt 

(7)Lag bolt 

(8)Machine bolt 

(9)Plow bolt 

(10) Sex bolt 

(11)Shoulder bolt 

(12)Square head bolt 

(13) Stud bolt 

(14)Timber bolt 

(15)T-head bolt 

(16)Toggle bolt 

(17)U-bolt 

(18) J-bolt

The role of bolts

The other end of the bolt should be screwed with a nut (that is, a screw cap) and then tightened to connect the two parts. The other bolt head is hexagonal. The nut, which is the screw cap, is used with the bolt. Bolt: A type of fastener consisting of a head and a screw (a cylinder with an external thread) that is to be fitted with a nut for fastening two parts with through holes. This type of connection is called a bolted connection. If the nut is unscrewed from the bolt, the two parts can be separated, so the bolt connection is detachable.

What is a nut?

A nut is a type of fastener with a threaded hole. Nuts are almost always used in conjunction with a mating bolt to fasten multiple parts together. The two partners are kept together by a combination of their threads' friction (with slight elastic deformation), a slight stretching of the bolt, and compression of the parts to be held together.

What are the types of nuts?

(1)Hex Nut

(2)Heavy Hex Nut

(3)Slotted Hex Nut

(4)Hex Castle Nut

(5)Acorn Nut

(6)Wing Nut

(7)Square Nut

(8)K-Lock

(9)Hex Thin Nut

(10)Flange Nut

(11)Nylon Insert Lock Nut

(12)Top Lock Nut

Nutm aterial

(1)Low or medium carbon steel

(2)Medium carbon steel Q&T

(3)Alloy steel Q&T

The role of the nut

In normal use, a nut-and-bolt joint holds together because the bolt is under 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 (also called a jam nut) can be used

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