Bolts and Screws are two unique mechanical fasteners used to hold two or more components together. Many believe that bolt and screw refer to the same fastening hardware as they look similar and possess quite similar features. Even in naked eyes, bolts vs screws seem to be the same as much difference between a bolt and a screw is not observed. But as per engineering applications and understanding, there are differences between bolts and screws. In this article, we will explore the characteristic features of bolts vs screws.
What is a Bolt?
A bolt is a mechanical fastener with a cylindrical threaded shaft used to assemble unthreaded objects. Usually, the term bolt refers to a fastener having only part of its shaft threaded. In general, a bolt is inserted through parts having unthreaded holes and then a nut is screwed to provide a clamping force and prevent axial movement.
The part of the shaft that is unthreaded is termed as ‘the shank’. The bolt head and nut prevent axial movement and the shaft of the bolt restricts radial movement of the parts. The unthreaded shank provides a more precise and less abrasive interface with the parts. At the same time, the shank does not contain stress concentrations due to being unthreaded.
What is a Screw?
A Screw is a mechanical fastener having threaded cylindrical or tapered shaft used to engage parts with threads. Screws with tapered shaft are self-threading means thread cuts into the material while the screw is turned. Screws have their entire shaft threaded.
The friction at the threads is the force that keeps the parts securely fastened. This friction is generated by the applied torque in the case of machine screws whereas for self-tapping screws the radial expansion of the hole creates a major part of this friction.
Bolts vs Screws: Differences between Bolts and Screws
Now that Bolts and Screws are clear, let’s find out the differences between them.
Bolts vs Screws-Construction
As per the construction of Bolts and Screws, Bolts usually have partially threaded uniform cross-sections but Screws can have tapered shafts. So the cross-section may vary according to the length of the screws. Also, for screws, the entire length is threaded.
Bolts vs Screws-Application
To secure a bolted joints, nuts are required whereas the screws works on its own without the requirement of nuts. Sometimes washers are also added in bolts.
During installation of a bolted joint the torque is applied at the nut whereas tfor screws the torque is applied at the screw.
Bolts are always used with un-threaded parts whereas Screws are used with threaded parts. In case the thread is not available, the self-tapping screws create those while installation.
Screws vs Bolts-Clamping Force
The nut and bolt assembly creates a very high clamping force keeping the member in between under compression. On the other hand, Screws are used where clamping force requirement is low.
Bolts vs Screws-Load Carrying Capability
The reliability of bolted joints is very high. Bolts can carry high loads. For increasing load carrying capabilities, larger size bolts are used in construction industries. But, Screws have a lower load-carrying capability and they are not available in larger sizes. The reliability of Screws is moderate.
Other differences between Bolts and Nuts
As nuts are used to tighten a bolt, the length of the bolts must be more than the width of the parts through which it is protruding. On the contrary, the length of screws is usually less than the width of the assembled components.
Bolts are usually fastened using a spanner or other tools whereas Screws are normally tightened using a screwdriver or a driver bit.
Removing a bolt is usually easier than removing a screw.
Cost of Bolts are usually higher than that of Screws. So, Bolting is costlier option whereas screws are cheaper.
A range of Bolts and Screws are available for engineering applications. Different types of Bolts include anchor bolts, arbor bolts, elevator bolts, hanger bolts, hex bolts, J bolts, lag bolts, rock bolts, shoulder bolts, and U bolts; which are available in a wide range of material like steel, stainless steel, brass, bronze, nylon, plastic, etc. Similarly, different types of screws are hip-board screws, particleboard screws, deck screws, drive screws, hammer drive screws, drywall screws, eye screws, dowel screws, wood screws, twin-fast screws, security head screws, and sheet metal screws; the material of these screws also vary depending on the application.