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Choosing the right screws for your project

From wood screws and self-tapping sheet metal screws to screws made for concrete, drywall, decks, and other materials, each type of screw is designed for a specific use. Here’s how to choose the right one.

Models of screws

Screw parts and features

Every screw has a head, thread, shank, and tip—every part has a particular purpose:

Here’s what you should know about screw design, materials, and finishes:

1. Head shapes

Screw heads come in four main shapes:

  • Flat: The head ends flush with the surface.
  • Round: Domed on top and flat underneath. Distributes load evenly when attaching metal to wood.
  • Oval: Designed to be partially countersunk, leaving a smooth, raised profile for a decorative effect.
  • Pan: Like a round head but with a flatter profile.

2. Head styles

  • Slotted: A single slot in the screw head.
  • Phillips: X-shaped slot allows more torque yet avoids over-tightening. Recesses come in different sizes; make sure you have the correct bit size for the screw.
  • Robertson: A Canadian innovation, Robertson heads have a tapered square recess. There are different sizes; make sure you have the correct bit size for the screw.
  • Special or proprietary: Torx, Allen, Star Drive, and other bit recesses are easier to drive and less prone to stripping.

3. Shank

The shaft of the screw.

4. Threads

Threads are considered coarse or fine. Coarse threads have steeper and more pronounced edges to bore into wood or metal; fine threads have shallower edges and more threads per inch. Common characteristics:

  • Single-helix thread: One revolution advances the screw one pitch (pitch is equal to 1 divided by the number of threads per inch).
  • Double-helix thread: Two threads are wrapped around the shank. One revolution advances the screw two pitch-lengths. This makes long screws easier and faster to drive (like a drywall screw).

Pro Tip

Machine screw threads are designated by the number of threads per inch, like bolt threads. An 8-28 machine screw has a #8 shank diameter and 28 threads per inch.

5. Length

The measurement depends on head type.

  • Flat head: Measure from the top of the head to the tip.
  • Round, oval, and pan head: Measure from the bottom of the head to the tip.

6. Diameter

The thickness of a screw can be expressed as a gauge (e.g. "#8," where the higher the number, the thicker the screw shank). #12 screws can have different lengths but will have the same thickness of shank. Diameter may also be listed in millimeters.

7. Finishes

Screws are plated or finished to improve their corrosion resistance or appearance. Common finishes are:

  • Bright finish screws are lightly polished and not coated. They will rust if exposed to moisture.
  • Hot-dipped galvanized screws are dipped in molten zinc to produce a rough, dull coating that resists corrosion. Recommended for outdoor projects and cedar, redwood, and treated lumber that require “ACQ-compatible” screws.
  • Zinc-plated (electroplated galvanized screws) are coated in zinc powder. The result is a bright finish that’s rust resistant but not for outdoor use.
  • Brass-plated and copper-plated screws will not rust, which makes them an attractive choice for outdoor projects, but they are not as strong as steel.
  • Blued screws are heat-treated until the oil is completely burned off, which increases holding power.
  • Deck screws are typically coloured brown or green and are made to withstand the highly corrosive chemicals in pressure-treated lumber. Look for the label “ACQ compatible.”
  • Drywall screws have a black phosphate coating that prevents wet drywall compound from corroding the screw head.

Pro's tip

Over time most people end up with a collection of fasteners. Whether you use the containers they came in, an organizer made specifically for screws or homemade containers, take care to keep screws organized so you don't have to go buy more every time you begin another project. One suggestion: glue a sample of each item to the outside of its box. You’ll be able to see at a glance what you have in stock and where it is.

Answers to the most frequently asked questions

Here are answers to the most frequently asked questions concerning the use of screws, as well as techniques and necessary tools.

How long should your screw be?

In general, a screw should go through the thinner piece of material so two-thirds of its shank is bored into the thicker piece of material.

When do you drill a pilot hole?

  • Drill a pilot hole if you’re using hardwood, thick screws, or wood that may split.
  • Use a drill bit that’s slightly smaller than the screw diameter.
  • If a hole is overly large, hammer in a golf tee and cut it off flush with the surface before driving in the screw.
  • Countersink drill bits produce both a pilot hole and a shallow, conical hole so the screw head can sit flush in the wood surface. Most countersink bits have an adjustable collar so you can control the hole depth and size.

How do you know what screwdriver to use?

  • If you use a power screwdriver, impact driver, or drill with a driver bit, use one with a clutch that will prevent over torquing the screw head and bit.
  • Invest in a set of properly sized screwdrivers and bits made from high-quality steel.
  • The right size bit will drive the screw more effectively and be less likely to strip the screw head. Cheap bits can damage the screw heads during use or simply wear out in a very short time.

How do you extract a screw with a damaged head?

To extract a screw with a stripped head, drill a small hole in the screw head and use a specially spiraled extractor bit. Its threads turn to the left to remove the damaged

How do you choose between steel, stainless and aluminum screws?

The choice of material always involves a compromise on strength, corrosion resistance, cost, and appearance.

  • Steel screws are the most common because of their strength and value but will corrode if left unfinished and exposed to moisture.
  • Stainless steel and aluminum are not as strong as mild or hardened-steel but will not corrode.

Suggested products

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