DIFFERENT TYPES OF NUTS AND BOLTS

 DIFFERENT TYPES OF NUTS AND BOLTS

 

A bolt contains two parts a shank and head. The cylindrical portion of the bolt is known as the shank. The shank is threaded at the tail end for a sufficient length so as to effectively engage with a nut.

The shape of the head is depended upon the purpose for which bolt is required. The nut is a type of a fastener which has a threaded hole in it. The nut is always used in joining with a mating bolt to fasten various parts together.

Different forms and types of nuts and bolts are as follows:

• Form of Bolts

1. Hexagonal-headed bolt
2. Square-headed bolt
3. Cylindrical or cheese-headed bolt
4. Cup-headed or round-headed bolt
5. T-headed bolt
6. Countersunk-headed bolt

Hexagonal-headed bolt

This is the most common form of a bolt and is used for general fasting purposes. The hexagonal head is chamfered at its upper end.

To prevent rotation of the bolt while screwing the nut on or off, the bolt-head is held by another spanner. A hexagonal-headed bolt illustrated in the figure.

Square-Headed Bolt

This bolt is commonly used when the head is to be accommodated in a recess. This recess is made of square shape so that the bolt is prevented from turning when the nut is screwed on or off.

When a square-headed bolt is to be used with its head projection outside, it is provided with a neck of square cross-section. This prevents rotation of the bolt. This bolt is commonly used in bearings for the shaft. A square-headed bolt is shown in the figure.

Cylindrical or Cheese-Headed Bolt

This type of bolt is used where projecting corners are unacceptable, and where the space for arranging the bolt-head is relatively limited. The rotation of the bolt is prevented by means of a pin inserted into the shank just below the head.

The projecting part of this pin fits into a corresponding groove in the adjacent piece. This bolt is commonly used in big ends of connectors, eccentrics, etc.

Cup-Headed or Round-Headed Bolt

This bolt is used when projecting are undesirable and where better appearance is required.

It is usually provided with a sung forged on the shank just below the head, as shown in the figure. To prevent rotation of the bolt. This bolt is it used in the construction of tanks and certain parts of locomotives.

T-Headed Bolt

This type of bolt is used for securing clamps, vices, and other accessories to the tables of machine tools.

The tables are provided with T-slots to accommodate the T-heads. The neck of this bolt is usually square in section to prevent rotation of the bolt A T-bolt is shown in the figure.

Countersunk-Headed Bolt

This form of a bolt is used where the head of the bolt must not project above the surface of the connection piece.

It may be provided with a snack or a neck to prevent rotation of the bolt.

• Special Purpose Bolts

1. Stove bolt
2. Carriage bolt
3. Hook Bolt
4. Expansion bolt
5. Foundation or rag bolt
6. Eye-bolt
7. Stud

Stove Bolt

A stove bolt has a round flat head which is beveled on the underside to fit a countersunk hole, it is provided with a slot on the head, as shown in the figure.

For screwing the bolt into a nut by means of a screwdriver. This is used for assemblies where precision is of no great importance, and it is desirable to have the head of the bolt flush with the surface of the work.

Carriage Bolt

This is used for fastening wooden parts together or for fastening metal parts to wood it has squared portion directly under the head to prevent rotating when the nut is tightened or slackened. A carriage bolt is shown in the figure.

Hook Bolt

The hook bolt, shown Fig. is used in semi-permanent fastening in concrete.

This is also used in cases where there is no room for a bolt hole through one of the pieces to be connected, or in cases where a bolt hole would seriously weaken a piece. So the hook bolt is used for attaching shaft hangers to the flanges of joists and girders.

Expansion Bolt

This type of bolt is used in attaching parts to brick, stone or concrete walls and floors hee bolt has an internally threaded split sleeve which is slipped into a hole made in the wall and then expanded by running in the screw. This is shown in Fig.

Foundation or Rag Bolt

The rag bolt, shown in Fig. is used for fixing into the stone concrete foundation, the head is wider at the bottom than at the top, and is led into a tapered hole.

The tapered head is cut in an uneven manner (jagged) and moulted lead or sulfur is poured into the taper hole to fill the space between the lead and the stone or the concrete as the case may be. Where great strength is required, four parallel bars or keys are used in addition.

Eye-Bolt

The eye-bolt, shown in Fig. is very commonly used for lifting purpose. It is screwed or turned inside a threaded hole on the top of the machine.

Electric motors and medium and lightweight machinery are equipped with one or more eye-bolt so that they may be readily lifted and moved by an overhead crane.

Stud

A stud is shown in Fig. consist of a plain piece of cylindrical steel which is screwed at both ends. It has no head like a bolt. The nut-end is threaded for a length slightly more than the thickness of a nut or nuts to be used.

The other end called the metal end. It is threaded for a length at least equal to the diameter of the stud. The stud is used in place of a bolt when a bolt. Stud is commonly used to cylinder covers engine cylinders.

• Forms of Nut

1. Hexagonal Nut
2. Square Nut
3. Ring Nut
4. Cap Nut
5. Cylindrical or Capstan Nut
6. Dome Nut
7. Wingnut or Thumb Nut

In order to Mack bolt and studs into effective fastenings, the nut is required. Nuts are usually in the form of hexagonal or square prisms. Besides these, the cylindrical and other form is used in a particular requirement.

Hexagonal Nut

This is the most common form of nut used for the general fastening purpose in conjunction with a hexagonal-headed bolt. A hexagonal nut is shown in Fig.

Square Nut

A square nut, shown in fig. is used in conjunction with a square-headed bolt. The spanner used for the nut can have a better hold on a square nut than on hexagonal nut.

Ring Nut

It is the form of a ring provided with slots in the curved surface for a special c-spanner. A ring nut is shown in the figure. These nuts are generally used in parts, one nut acting as a lock nut the other.

Cap Nut

It is a hexagonal nut provided with a cylindrical cap at the top to protect the end of the from corrosion. It also prevents leakage through the threads. Cap nuts commonly used in smoke-boxes locomotives.

Cylindrical or Capstan Nut

This nut is cylindrical in shape and has holes drilled in the curved surface for turning it with a tommy bar.

Dome Nut

It forms the cap nut having a special dome at the top as shown in the figure.

Wingnut or Thumb Nut

A wing nut is shown in the figure. This nut can be easily operated by the thumb and a finger and is used where it is required to be adjusted frequently.

Locking of Nuts

When a nut is tightened over the bolt, a small working clearance exists between the threads of a nut and bolt even in the highest class of fits.

The types of nuts and bolts used in the moving parts of machinery will be subjected to continuous vibration and in addition, sometimes, required to carry varying axial load also, for example, as the crossheads and connecting rods of an engine.

Under such conditions because of the working clearance existing between the mating threads, the nut develops a tendency to work loose or unscrew by itself.

This consequently may result in a serious breakdown. To prevent this, some means of locking the nut from unscrewing is necessary. The various locking devices for nuts are classified into positive and friction types. However, the tendency of unscrewing is reduced if the threads of the nut and bolt are of the good fit.

The positive methods of locking make use of a split pin, or a screw, or a lock plate, or a tab washer to lock the nut. In the friction method either an additional nut called lock nut, or a spring washer is used to lock the nut.

Split Pin Locking

The simplest method of locking a nut using a split pin is shown in the figure. After the nut has been finally tightened, a small hole is drilled through the blot close to the top face of the nut. The split pin is then inserted in the hole and the split ends of the pin are opened so as to prevent it from coming out while in use.

The main objection to using this type of locking is that the hole drilled in the blot reduces its strength considerably. The other equally important objection is that after continuous use swing to the stretch of the bolt the split pin may not rest on the top face of the nut which may reduce the locking effect.

Set Screw Locking Using Grooved Nut

A hexagonal nut provided with a cylindrical grooved collar at its the lower end is called Penn to ring or grooved nut. The end of the bolt hole is counterbored to receive the cylindrical lower grooved portion of the nut as shown in the figure. Locking of the nut is done by a set screw screwed through the nearest face of the workpiece.

The projecting dog-end of the set-screw enters the groove in the cylindrical portion of the nut and prevents the slackening of the nut. This method of locking is possible if the bolt hole is close to the nearest vertical edge as in the case of the marine engine connecting rods.

When the bolt hole is not close to the vertical edge of the workpiece, this nut is used in conjunction with a separate collar as shown in the figure. The dowel pin screwed in bearing surface prevents the rotation of the collar.

Locking By a Lock Plate

This type of locking is employed in heavy engineering work, as in the case of connecting rods, wheel shaft etc. The empirical proportions of the lock plate are shown in the figure. Initially, the nut is tightened and then the lock plate is inserted through the nut.

The plate is grooved in such a way that the grooves in the plate receive the hexagonal corners of the nut at every 30° rotation. The plate is fixed to the bearing surface by a tap bolt screwed into it. The figure showed the assembly of the locking of a nut by the lock plate. Since the nut is held tight within the grooves of the lock plate, the nut is prevented from slackening.

Locking By a Tab Washer

A washer provided with a rectangular projection is called the tab washer. This method of locking of nut or bolt head is suitable when the nut or bolt head is placed near the vertical edge of the workpiece.

After the nut is tightened the tab and the projecting portion of the washer itself are bent to bear against the vertical surface of the workpiece and one of the lateral faces of the nut or, the bolt head.

Locking By a Lock Nut

In the type of locking, the friction between the mating threads of bolt and nut locks the nut. When the nut is tightened over a bolt, the lower flanks of the threads of the bolt will be in contact with the upper flanks of threads of the nut.

When another nut is screwed down hard over the lower nut, it tends to pull the bolt through the lower nut. This virtually makes the upper nut to take up all to load, While the lower nut to function simply as a washer since there will not be any contact between the threads of the bolt and the lower nut.

Now the upper nut is held by a spanner While the lower nut is pull in the opposite direction. This cause the lower flanks of threads of the lower nut to come in contact with the upper flanks of the threads of the bolt causing a wedging action between them.

This makes the lower nut to act as a lock nut. Theoretically, the lower nut which is a lock nut may be the thin nut as shown fig. But as it required a special thin spanner to turn it, in practice it is more usual to place taking nut below the lock nut as shown in Fig. such cases sometimes two nuts of equal thickness are used as shown in Fig.

Locking By Spring Washer

In this method of locking a coiled spring, the washer is placed underneath the nut as shown in Fig. when the nut is tightened, the spring force of the spring exerts an axial force on the underside of the nut and holds it by the friction grip. This prevents the slackening of the nut.

A single coiled spring washer will be sufficient for light classes of work. When the vibrations are high either a double coiled or triple coiled spring washer is used.

Screw Pin Locking

A nut may be locked by a screw pin, screwed in the bearing surface adjoining the nut touching one of the lateral faces of the nuts as shown Fig. This type of locking is employed when the nut is expected to remain without any adjustment for a long time.

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