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Bolt, Nut & Washer

Updated: Oct 21, 2020

What is bolt, nut and washer?

The main purpose is to mechanically connect and fix two or more parts together. According to the difference in type, quality, shape, and material will significantly affect the performance and service life of the fastener. The bolt is composed of a head and a cylinder with screw threads for part of its length. The nut is used in conjunction with a matching bolt to fasten multiple parts together and nut is a female member of pair with internal threads to match the bolt. Washers used to prevent loosening and crushing.

They can be manufactured by aluminum, brass, copper, steel, stainless steel, and so on depends on what kinds of projects they will be used for.


The Difference between bolt, nut, and washer


A bolt is a mechanical fastener which has multiple configurations to suit different materials and strength requirement. Bolt usually has an external thread and join with a nut to connect those parts. Bolt is consist of a head and a shank. The head can be different shapes based on the usage purpose. The shank is the cylindrical and unthreaded part of the bolt between the head and the threaded portion that can prevent the movement of parts.

Type of bolts

  1. Anchor bolt: Used to attach a structural member or component to a concrete slab or poured foundation. Embedded in concrete or masonry.

  2. Carriage bolt: domed or countersunk head with the square section under the head grips to prevent from turning when the nut is tightened. Normally used to tighten on metal to timber.

  3. Flange bolt: integrated flange that serves as a washer to distribute the bearing load.

  4. Plow bolt: Due to its durability, which is ideally used for heavy-duty applications such as construction or industrial machinery. The flat countersunk head and square shank neck.

  5. Hexagon bolt: As known as Hex tap bolt. A hexagonal head shape has six sides. Driven with a wrench. Many lengths and threading varieties. Tighter tolerances

  6. Square head bolts: square head bolts are defined by their head shape which has four-sided. Usually with a short shank. Easier installation due to its head shape that allows for a wrench to grip easily.

  7. Socket head cap screw: Head style is various from flat head countersunk to a knurled cylindrical sides. It is driven and tightened with an Allen wrench or hex socket tool.

  8. T-Head Bolt: Head with T-shaped that can be inserted into a groove or a notch to secure the bolt in place and avoid rotation when tightening the nut.

  9. Other bolt types such as blind, eye, hook, J, U, countersunk, lag, and shoulder.


A nut is a fastener with an internally threaded hole and is usually attached with a bolt to prevent loosening and movement. It has a variety of shapes, sizes, materials, and thread patterns. When selecting a nut, it will be constrained by your choice of bolts.

Type of nuts

  1. Cap nut: Its name is defined by its shape. It can prevent contact with the external thread with a domed top.

  2. Coupling nut: It looks longer, cylindrical nut that joining two male threads.

  3. Flange nut: Similar to flange bolt. Its wide flange can act as an external washer, however, it is fixed and unable to spin. It allows distributing the load to prevent loosening.

  4. Hex nut: Hexagonal shaped with six-sided. Versatile and driven with a wrench when installation. Such as hex finish, semi-finished hex, hex flange, etc.

  5. Lock nut: It has a variety of shapes and usually requires a greater torque to secure and resist loosening when vibration condition.

  6. Slotted hex nut: Using a cotter pin or safety wire to create a locking mechanism.

  7. Square nut: Square shapes that increase the amount of friction, reduce loosening.

  8. Wheel nut: Normally used in automotive wheel application.

  9. Additional nut types such as castle, conical, heavy hex, Keps k lock, knurled thumb, nylon hex, square, and wing.


A washer is a disk-shaped thin component with a hole in the center that can enhance control over-locking and friction when used with other fasteners. Washer usually serves as a spacer at preventing the loosening of the fasteners assembly and also distributes the force or load of screw and nut. The washer should be complementary to your selected bolt and chosen to suit your unique fastening application.

Type of washers

  1. Beveled washer: Slightly angled on its bearing surface, allow to join the materials that are uneven or imperfect to one another. It is usually used in the I-beam, channel, and other structural applications.

  2. Flat washer: The most common type in the plain washer and various thicknesses. Round shape and a hole in the center to accommodate a bolt. Due to the larger surface area for better load distribution. Different thicknesses to hold a variety of strength.

  3. Lock washer: There has many shapes. To secure fasteners and prevent slippage of fasteners. Used in a high level of vibration. Includes split ring, high collar, external tooth, internal tooth.

  4. Structural Washer: The most heavy-duty washer. Thick and strong to withstand high load pressure. Usually used in heavy-duty applications.

  5. Square Washer: Shape with a square. Either flat on both sides or one side flat and another side are beveled. Used with Square head bolts. Can withstand and hold stronger than the flat washer.

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