Choosing Self-Tapping ScrewsMaryLouise Eckman

Choosing the right screw can feel challenging when you don’t know what the different heads, shanks and points can do. By understanding these aspects, you will be able to find the best self-tapping screw for your project without having to ask for assistance.

Explore Head Types

The screw head you use will affect the stress distribution and finish of your project. Common head types include:

• Hex washer: This hex-shaped head is best used for heavy-duty applications, like roofing. It can also come with a neoprene washer for more stable fastening.
• Modified truss: A big domed head with a flange creates a larger bearing surface with a low profile.
• Oval: This screw has a countersunk bottom and rounded decorative head.
• Pan: This type features a domed head with straight sides, and it’s often used for high-torque applications.
• Flathead: This screw has a flat top that sits below the surface for a clean finish.
• Bugle: A countersunk head, flat top and concave bearing face allow these screws to distribute stress over a larger area than a flathead screw. Drywall contractors use these for attaching plasterboard and wood to metal studs.
• Pancake: When you need an unobstructed head and large clamping area, the pancake screw is the right choice. The large head distributes stress across a wider area.

Consider the Shank Size

The shank is the threaded shaft of the screw, and different sizes offer various qualities. You’ll see shank sizes listed as a number without a unit of measure. The larger the number, the larger the shaft diameter. Hex Washer Head sizes often have standard shaft sizes to accommodate typical applications. These standards are:

• 1/4″ Hex Head = #6 or #7 or #8 shank size
• 5/16″ Hex Head = #10 or #12 shank size
• 3/8″ Hex Head = #14 shank size

While these are industry standards, there are exceptions. For example, zip screws for the gutter industry use a high profile 1/4″ hex head with #10 shanks. In the 1980s, #8 shanks were standard for gutter applications, but with the change in wood quality, #10 shanks respond better to knots today. Our hex head gutter screws also have a filet for extra strength.

Think About Threads Per Inch

Threads are the spiral shape around a screw’s shank. The threads per inch (TPI) affect how effectively a screw works through a material. Generally, a lower TPI is better for softwoods, and a higher TPI is better for metal and hardwoods.

Threads per inch are a clear example of why choosing the right screw is essential for your project. Any screw can snap if it experiences too much force.  The threads are finer (more threads per inch) when you go into harder woods or metal so that the screw penetrates slower, otherwise, the screw will snap.  Most users think that they received ‘bad’ screws when they actually just have the wrong screw for their application. The right TPI can ensure smoother fastening and fewer wasted screws.

Choose Your Screw Point

A screw’s point affects how it interacts with metal during initial material entry. The most common types of screw points are:

• Needlepoint: These screws feature twin lead threads and sharp points for self-piercing in light sheet metal.
• Drill point: Rather than a sharp point, drill points have a wide, blunter tip. The bulkier end makes it easier to insert these screws on initial impact. These screws are helpful for a range of construction applications, though they are not recommended for roofing.

While these are the two general point categories, there are other specialty points for specific applications. For example, type 17 screws have a fluted point for capturing wood chips and preventing splits.

Pick a Plating

The plating will affect how your screw interacts with its environment. Zinc plating is standard for most interior screw applications, and it can last up to two years. Hot-dipped and mechanical galvanized screws can last up to five years. These two types are the traditional plating styles, but other types include:

• Ceramic: This plating resists rust and comes in 500-, 1,000- and 1,200-hour salt spray tested options. These screws are well-suited for outdoor applications where the fasteners will have to withstand different types of weather.
• Stainless steel: As another rust-resistant option, stainless steel screws are also ideal for outdoor applications. All Points Fasteners offers both magnetic and non-magnetic styles.

Read the Labels for Screw Types

Now that you know how to choose the right screw for your application, you need to know how to find it based on the label. Self-tapping screws will have a label that reads “8-18×1 HWH SDS Z/P.” In order, the label means:

• #8 shank
• 18 TPI
• 1 inch long
• Hex washer head
• Self-drilling screw
• Zinc plating

Turn to All Points Fasteners When Choosing Screws

Explore our screws index today, and request a quote to receive more information.