Bolt vs Screw: How to Choose the Right One For the Job

Bolts are an externally threaded fastener designed to be paired with nuts and washers to create a secure bond between all sorts of different material types. The three basic types are carriage bolts, stove bolts, and machine bolts. Other types include the masonry bolt and anchor, toggle bolt, and expansion bolt, which are used to distribute weight when fastening something to a hollow wall [source: Monroe Engineering].

Machine bolts are manufactured in two gauges: fine-threaded and coarse. Carriage and stove bolts are coarse-threaded. Bolt size is measured by shank diameter and by threads per inch, expressed as diameter by threads (for example, 1/4 X 20).

Carriage bolts are available up to 10 inches long, stove bolts up to 6 inches, and machine bolts up to 30 inches. Larger sizes usually must be special ordered.

Here are some of the more common bolts to keep in your toolbox:

Carriage Bolt

Carriage bolts are used mainly in making furniture. They have a round head with a square collar and are tightened into place with a nut and wrench. The collar fits into a prebored hole or twists into the wood, preventing the bolt from turning as the nut is tightened. Carriage bolts are coarse-threaded and are available in diameters from 3⁄16 to 3/4 inch and lengths from 1/2 inch to 10 inches.

Stove Bolt

Stove bolts aren't just for stoves; they are quite versatile and can be used for almost any fastening job. They are available in a wide range of sizes, have a slotted head -- flat, oval, or round, like screws -- and are driven with a screwdriver or tightened into place with a nut and wrench.

Most stove bolts are completely threaded, but the larger ones may have a smooth shank near the bolt head. Stove bolts are coarse-threaded and are available in diameters from 5⁄32 to 1/2 inch and lengths from 3/8 inch to 6 inches.

Machine Bolt

Machine bolts have either a square head or a hexagonal head. They are fastened with square nuts or hex nuts and are wrench-driven. Machine bolts are manufactured in very large sizes; the bolt diameter increases with length. They are either coarse-threaded or fine-threaded and are available in diameters from 1/4 inch to 2 inches and lengths from 1/4 inch to 30 inches.

Hollow Wall Bolt

Toggle bolts and expansion bolts are used for fastening lightweight objects, such as picture frames, to hollow walls. Toggle bolt wings are opened inside the wall by a spring.

Expansion bolts are inserted into an expansion jacket, which expands as the bolt is tightened. The bolts are available in diameters from 1/8 to 1/2 inch and lengths up to 8 inches for walls as thick as 13/4 inches.

They may seem simple, but screws work using a combination of rotational motion, torque, and linear force to bond things together permanently. Screws are an externally threaded fastener capable of creating a secure grip without the need to locate a suitable nut. Instead, they require a tapped hole, or a threaded hole, that features a preformed internal thread designed to match the screw's unique spiral pattern [source: Dale].

Here are some of the more common screws to keep in your toolbox:

Sheet Metal Screws

sheet metal screws are unique in that they have threading covering every part of the shank. This fully threaded design make them idea for use with sheet metal.

Machine Screws

A catch-all term used to describe a variety of fastener types, machine screws are most often found with blunt-ended tips and are fully threaded, all the way to the head of the screw [course: Britannica].

Wood Screws

These common, sharp-pointed screws are available in all sorts of sizes, and are the ideal way to pull and secure wood material together. Most wood screws feature an unthreaded shank near the head of the screw.

Now that you have a better understanding of the difference between a bolt and a screw, and are familiar with a variety of the applications of each, you should have what you need to be able to select the right one for your project.

And if you still don't get it, that's OK too. Describe your project to a local tool professional and they should be able to point you in the right direction.