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The Difference Between a Bolt & a Cap Screw

Different sizes of bolts
bolt image by martini from Fotolia.com

It is sometimes difficult to differentiate between bolts and cap screws as these terms are often used interchangeably. When we pay close attention, both of these fasteners are quite different from the manufacturing and application point of view. Understanding these differences can help us in sorting out different tools and making sure the right type of fastener is applied.

Tightening Mechanism

A bolt has a head that can be tightened and loosen with the help of a hex or square wrench or a spanner. If the fastener is tightened and loosen by a drive tool that has to be inserted into the head, then it is a cap screw. In order for the bolt to be tightened, it requires a kind of nut that keeps it tight but in the case of a cap screw, it does not require any sort of nut and can be used on its own.

Fixed Position

Bolts usually hold and compress the material as there is a nut or washer involved. Whereas a cap screw is held and compressed by the material it is fixed to such as wood, metal, plastic or cement. In a fixed position a bolt is harder to rip out, whereas a cap screw is easier because there is no nut fixed on the other side.

Head Shape

A shank between the head and the threads of a cap screw and a thin spacer under the head helps the cap screw rotate. The height of the head of a cap screw is slightly smaller than a bolt. Cap screws have round heads, unlike bolts that have square heads that can be wrenched easily.

Manufacturing Process

Bolts are typically manufactured by a hot forging process, whereas a cold heading process manufactures cap screws. Bolts have a reduced diameter of the body which is not less than the minimum pitch diameter of the thread. Cap screws have a head that has a bigger diameter than the threaded portion of cap screw, this provides a mechanism stop when the screw is tighten. The hole in which a cap screw is tightened has internal thread that equals to the external thread. This helps the screw to advance until it is fully tight.

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