Types of Screws
A screw is a threaded fastener that holds materials together by turning into them. It sounds simple, but the "screw" family is huge, and picking the wrong type is the fastest way to get a stripped head, a split board, or a joint that works loose. This guide covers the most common types of screws, how they differ, and how to choose the right one for the job.
What Is a Screw?
A screw is a fastener with a helical thread that cuts or forms its own path into a material. Most screws are driven with a screwdriver or bit, and the thread does the holding. That is the key difference from a bolt, which is usually tightened with a nut. If you are not sure which one you need, our bolt vs screw guide explains the difference.
Wood Screws
Wood screws are designed for timber. They have a tapered body and a sharp point, so they bite into wood without a pilot hole in many cases. Coarse threads hold well in softwood, while finer threads suit hardwood. Common head styles are flat-head (countersunk) and round-head, and most wood screws are made of carbon steel or stainless steel for outdoor projects.
Machine Screws
Machine screws have a straight, uniform thread and a flat tip. They are not self-tapping: they thread into a pre-tapped hole or into a nut. You will see them everywhere in metal-to-metal assembly, electronics and machinery. Sizes are usually described by diameter and thread pitch, such as M4 × 0.7 or #8-32.
Self-Tapping Screws
Self-tapping screws form or cut their own threads as they are driven, so no pre-tapped hole is needed. They are common in sheet metal, plastic and light assembly. Within this group, self-drilling screws go one step further and drill their own pilot hole, which speeds up metal-to-metal fastening on site.
Lag Screws (Lag Bolts)
A lag screw, also called a lag bolt, is a heavy-duty fastener with a coarse thread and a hex head. It is driven with a wrench rather than a screwdriver and is used for high-load connections in wood, such as decks, beams and heavy framing. Despite the name, it behaves more like a bolt than a screw. Browse our lag bolts for galvanized and stainless options.
Sheet Metal Screws
Sheet metal screws have sharp, fully threaded shanks made to fasten thin metal sheets. They are self-tapping and usually have a pan, flat or hex head. They are widely used in ductwork, panels and light metal fabrication.
Drywall Screws
Drywall screws are fine-threaded (or coarse-threaded, for wood studs) screws with a bugle head that sits flush without tearing the paper. They are hardened and phosphate-coated, and they are the standard choice for hanging plasterboard.
Screw Head Types
The head determines how the screw sits and how it is driven:
- Flat head (countersunk): sits flush with the surface.
- Pan head: rounded with a flat underside, used when the screw sits above the surface.
- Round head: domed for a finished look.
- Hex head: driven with a wrench or socket for high torque, common on lag bolts.
- Truss head: a wide, low profile that spreads clamping force.
Screw Drive Types
The drive is the recess in the head where the tool fits:
- Phillips: cross-shaped, very common and easy to find.
- Slotted: straight groove, traditional but easy to cam out.
- Torx (star): six-point star, resists cam-out and suits power tools.
- Hex socket: recessed hex, driven with an Allen key.
- Square (Robertson): self-centering, popular in woodworking.
Screw Materials and Finishes
Material affects strength and corrosion resistance. Carbon steel is strong and inexpensive, and it is usually zinc-plated for mild corrosion resistance. Stainless steel resists rust and is the right choice for outdoor, marine or food-contact use; 304 is general-purpose and 316 adds saltwater resistance. Other finishes include hot-dip galvanizing for heavy outdoor exposure and black oxide for appearance.
How to Choose the Right Screw
Work through these questions in order:
- What material are you fastening? Wood, metal, plastic or drywall.
- What load will the joint carry? Heavier loads need larger diameters or lag bolts.
- Will it be exposed to moisture? Choose stainless steel or galvanized.
- Do you need a flush finish? Choose a countersunk head.
- Will it be removed later? A machine screw with a nut is easier to service.
When in doubt, match the screw to the material first, then check the load and the environment.
FAQ
What are the most common types of screws?
Wood screws, machine screws, self-tapping screws, sheet metal screws and drywall screws are the most common. Each is shaped for a specific material.
How do I measure a screw?
Measure the overall length and the major diameter of the thread. Metric screws are listed by diameter and pitch (M4 × 0.7), while inch screws use a gauge number (#8, #10) and threads per inch.
What is the difference between a screw and a bolt?
A screw is usually driven directly into a material and relies on its threads, while a bolt is typically tightened with a nut. See bolt vs screw for the full comparison.
Which screws are best for outdoor use?
Stainless steel or hot-dip galvanized screws are best outdoors because they resist corrosion. Match 316 stainless for marine environments.
Get the Right Screws for Your Project
SolidLink manufactures screws, bolts, U-bolts, eye screws and other fasteners in carbon steel, stainless steel and galvanized finishes, with custom sizes and bulk quantities available. Browse our fasteners category or contact us for a quote.
