Bolts are a type of fastener. Fasteners are used to join feet. There are many types of bolts and hardware nuts. Most, if not all, type of bolt have machine threads.
A threaded bolt screws in to the nuts to hold or fasten. Bolt types include eye bolts, wheel bolts, and machine bolts, while types of nuts include cap nuts, expansion nuts, and u-nuts.
The type of material and finish also affect how types of fasteners look and perform. This guide is helpful to know about the types of nuts and bolts and the different types of bolt heads.
Nuts and Bolts Types
A bolt consists of two parts, the shank and the head. The cylindrical part of bolt is known as the shank. It is threaded to a sufficient length at the tail end for effective engagement with a nut.
The shape of head is determined by the work on which the bolt is required. A nut is the name given to the class of fasteners having a threaded hole in them. The nut is always employed in conjunction with a mating bolt for fastening various parts together.
Types of Bolts
Different forms and types of bolts are as follows:
- Hexagonal-headed bolt
- Square-headed bolt
- Cylindrical or cheese-headed bolt
- Cup-headed or round-headed bolt
- T-headed bolt
- Countersunk-headed bolt
- Stove bolt
- Carriage bolt
- Hook Bolt
- Expansion bolt
- Foundation or rag bolt
- Eye-bolt
- Stud
#1. Hexagonal-headed Bolt.
This is the most frequent form of bolt, and it is used for general fastening purposes. The head is hexagonal, and is chamfered at its upper end.
Another spanner holds the head of the bolt, a hexagonal-headed bolt being the one illustrated, but to prevent the bolt from rotating when screwing the nut on or off.
#2. Square-Headed Bolt.
This bolt is used when the head shall be sunk into a recess. This recess is of square shape so as to prevent the turning of the bolt when the nut is screwed on or off.
When it is required to use a square-headed bolt with the projection of its head outside, it is provided with a neck of square section preventing the turning of the bolt. This bolt is used for the bearings of the shaft.
#3. Cylindrical or Cheese-Headed Bolt.
This types of bolt is employed when a projecting corner is undesirable, and there is not sufficient room where the bolt head is to be located. The rotation of the bolt is prevented by the fitting of a pin into its shank just below its head.
The projecting portion of this pin fits into a corresponding groove in the adjoining piece. Bolts of this type are often used in the big ends of connectors, eccentrics, etc.
#4. Cup-Headed or Round-Headed Bolt.
This bolt is employed where projecting is objectionable and where a better appearance is desired.
It is usually furnished with a sung forged on the shank just below the head. To prevent the rotation of the bolt. This bolt is used in the construction of tanks and some parts of locomotives.
#5. T-Headed Bolt.
T-Bolt is a fastener that is designed to provide a secure means of attaching and holding vices, clamps, and other equipment to a machine tool table. The T-bolts are inserted into the T-slots that exist in the machine tool tables.
#6. Countersunk-Headed Bolt.
This form of bolt is used when the head of the bolt must not project above the surface of the connection piece. It may be formed with a snack or a neck to prevent the bolt rotating.
#7. Stove Bolt.
The head of the stove bolt is a round flat head beveled on the underside for a countersunk hole; the two sockets or slots in the head are for a screw driver.
For screwing in the bolt when the occurs use the screw driver. This is used for assemblies where they do not have to be very true, and where the head of the bolt is desired to be counter sunk with the surface of the work.
#8. Carriage Bolt.
Used to connect wooden materials or to connect metal materials with wooden materials, it has a square nut located directly underneath the quick-release clip that does not rotate when tightened or loosened.
#9. Hook Bolt.
Hook Bolt is used for semipermanent fastening in concrete, and is also employed, where there is not room for a bolt hole through one of the pieces to be connected, or where a bolt hole would sensibly weaken a piece.
The former is a common use of the hook bolt, which is so employed for attaching shaft hangers to the flanges of joists and girders.
#10. Expansion Bolt.
With this type of bolt parts may be secured to walls and floors of brick, stone, or concrete. The bolt is provided with an internally threaded split sleeve which is slipped into a hole in the wall and then expanded by running in the screw.
#11. Foundation or Rag Bolt.
The rag bolt serves for fixing 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 unevenly (jagged), and molted lead or sulfur is poured into the taper hole to fill up the space between the lead and the stone or the concrete—that is, whichever it happens to be. Where great strength is required, four parallel bars or keys are also used.
#12. Eye-Bolt.
The eye bolt is a common lifting bolt. It is sunk or turned into a thread on the top of the machine.
Electric motors, and medium and light weight machines, are provided with one or more eye bolts, so that they may be readily lifted and transferred by an overhead crane.
#13. Stud.
A stud is a plain piece of cylindrical steel, threaded at each end and without the head of a bolt. The nut end is threaded for a length slightly greater than the nut or nuts to be used thereon.
The other end is called the metal end, and is threaded for a length at least equal to the diameter of the stud. The stud is used instead of a bolt where a bolt. Stud commonly used to cylinder cover engine cylinders.
Types of Nuts
In order to make bolt and studs into effective fastenings, the nut is needed. Nuts are usually in the form of hexagonal or square prisms. In addition to these, the cylindrical and other form is used for a particular requirement.
- Hexagonal nut
- Square nut
- Ring nut
- Cap nut
- Cylindrical or capstan nut
- Dome nut
- Wingnut or thumb nut
#1. Hexagonal Nut.
This is the most usual form of nut for the general fastening purpose in combination with the hexagonal headed bolt.
#2. Square Nut.
A square nut, as shown in fig., is used in combination with a square-headed bolt. The spanner used for the nut can have a better hold on square nut than on a hexagonal nut.
#3. Ring Nut.
It is of the form of a ring with slots on the curved surface for a particular spanner. These nuts are generally used in pairs, one acting as a locknut, and the other.
#4. Cap Nut.
It is a hexagonal nut to which is attached a cylindrical cap at the top for protecting the end from corrosion. It also prevents leakage of gases through the threads. Cap nuts are frequently used in smokeboxes locomotives.
#5. Cylindrical or Capstan Nut.
It is a cylindrical nut having holes drilled in the curved surface so that it may be turned through with a Tommy bar.
#6. Dome Nut.
It consists of the cap nut provided with a special dome at the top as shown in the figure.
#7. Wingnut or Thumb Nut.
A wingnut is shown in the figure. This nut can be easily acted upon by the thumb and finger, and is employed when frequent adjustment has to be made.
Methods of Nut Locking
#1. Locking of Nuts.
When a nut is tightened over the bolt, a slight working clearance exists between the threads of nut and bolt, even in the highest class of fits.
The nuts and bolts in the moving parts of machinery will be subject to constant vibration. Sometimes they also have to be made to carry varying axial loads as, for example, the crossheads and connecting rods of an engine.
Under such conditions, on account of the working clearance existing between the applied threads, the nut tends to work loose or unscrew by itself. This would in some cases result in a serious breakdown, and in order to prevent this, some means of locking the nut from unscrewing is necessary.
The various locking devices for nuts are known technically as positive or else as friction types. However, the tendency of unscrewing is minimised if the threads of the nut and bolt are of a good fit.
In the method of positive locking a split pin, a screw, lock plate, or tab washer is used to lock the nut. In the friction method an extra nut called a lock nut, or else a spring washer is employed.
#2. Split Pin Locking.
The method of using a split pin for locking a nut in the simplest form is seen in the figure. After the nut is finally tightened a small hole is drilled through the blot close to the top face of the nut.
The split pin is inserted in the hole and the split ends are opened out, so that while in use it will not work out of the hole.
The paramount disadvantage of this locking system is that the hole in the blot obviously weakens it considerably.
Another equally serious disadvantage is that when used continuously, the swing due to the elongation of the bolt may not bring the split pin on the top face of the nut, thus weakening the locking effect.
#3. Set Screw Locking Using Grooved Nut.
A hexagonal nut with a cylindrical grooved collar at the lower end is called Penn to ring or grooved nut.
The end of the bolt hole is stepped or counterbored to the same depth as the cylindrical lower grooved portion of the nut.
The locking of the nut is affected by a set screw screwed through the nearest face of the work, to go into the groove of the nut and prevent the slackening of the nut.
A locking of this kind is valuable only where the bolt hole is as close as possible to the nearest vertical edge, as in the marine engine connecting rods; but where the bolt hole is remote from the vertical edge of the work, this nut is coupled with a collar. A dowel pin is screwed into the bearing in order to prevent the turning of the collar.
#4. Locking By a Lock Plate.
This method of locking is used for heavy engineering work, such as connecting rods, wheel shafts, &c., and the empirical proportions of the lock plate are as shown in the figure. The nut is first tightened, and then the lock plate is slipped through it.
The plate is grooved in such a way that at every 30° turn the hexagonal corners of the nut drop into the grooves of the plate.
This plate is held in position on the bearing by a tap bolt which is screwed into it. The accompanying diagram shows the arrangement for locking a nut by means of a lock plate. As the nut is wedged tightly into position in the grooves of the lock plate it cannot slacken.
#5. Locking By a Tab Washer.
A washer which has a rectangular projection is termed a tab washer. This locking arrangement of nut or bolt head is convenient when the nut or bolt head is near the vertical edge of the workpiece.
After the nut has been screwed home to a firm bearing, the tab, and the projecting portion of the washer itself, are bent over on the vertical side of the workpiece and one of the lateral faces of the nut or the bolt head.
#6. Locking By a Lock Nut.
In this kind of locking, friction between the faces of the flanks of the corresponding threads of the bolt and nut locks the nut. If the nut be screwed up upon a bolt the flanks on the lower face of the threads of the bolt will touch the upper face of the threads of the nut.
If another nut be set down hard upon the lower nut it tends to pull the bolt straight through the nut. This practically makes the upper nut take up all to load, while the lower nut acts merely as a washer, as there will be no contact between the threads of the bolt and nut.
Now the upper nut is held by a spanner, while the lower nut is pulled in opposite direction. This causes the lower flanks on the threads to come in contact with the upper flanks on the thread of the bolt, causing a wedging action between them and making the lower nut act as a lock nut.
Theoretically the lower nut which is a lock nut may be the thin nut but as it requires a special thin spanner to turn it, it is in practice more usual to place the taking nut underneath the lock nut as shown in Fig. in such a case, two nuts of equal thickness are often used.
#7. Locking By Spring Washer.
In this method of locking a coiled spring, the washer is placed underneath the nut. 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.
#8. 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. This type of locking is employed when the nut is expected to remain without any adjustment for a long time.