Your Guide to Choosing a Fastener
How to Select a FastenerSelecting the right fastener is critical to the success of its application and to your project. Consider these factors when selecting the safest and the best fastener for your project:
- Similar types; do not mix nails and screws in the same connector.
- Application or process
- Corrosion resistance
Size MattersA common method representing nail sizes is the penny size, which is a length designation. The length of a nail, from the head to the tip of its point, is defined as the “penny.” Size is written with a number and the abbreviation “d” for “denarius” which is Latin for “penny.”
While referring to penny size and type designations such as “box” or “common” is a typical method for calling out nails, it is more accurate and reduces potential confusion to always call the nail by diameter and length.
Diameter and Length are ImportantThe International Building Code® (IBC) evaluates and rates specific fasteners to be installed with specific connectors. But there can be subtle differences between what was specified and what was installed because the diameter and length may not be provided with the fastener type. For example, most hangers use 10d common nails as fasteners, per ICC reports. But installers may not know there are subtle differences in length and diameter between a common 10d nail and a 10d sinker, 10d pneumatic and 10d box nail.
Even though wood buildings have repetitive and redundant members, and most connectors are designed to support loads that exceed the service loads placed upon them, the differences can create more deflection and movement as well as increased damage from wind or seismic events. Suddenly, size turns into a safety issue that could have catastrophic results.
Also, non-structural nails, such as nails for components and cladding, should NEVER be used in structural connectors. Screws should ONLY be used if specifically engineered to be used with structural connectors.
Selecting the Right TypeA bolt is a bolt, right? Wrong. Just like we read above that not all nails are the same, the same applies to other fasteners. Take the bolt. A bolt consists of a head, shaft, and threaded end. Once you know what the bolt will be used for, you have to make decisions based on:
- Head: hex, screw, socket, or another design? The head design accounts for the amount of torque the bolt will take.
- Shaft length is also based on application.
- Threads: coarse (UNC), fine (UNE) or 8 thread (UN; mostly used in oilfields). Threads have a heavy responsibility; they carry the load. Coarse threads are quicker to assemble, and while fine threads take longer to install because they require more revolutions, they provide a more secure connection with stronger tension.
Common Nail TypesHere are the most common types of nails, usage, and their advantages.
Brads: Common name for nails less than 1 ¼" length with a head larger than the shank, basically a very small finishing nail. Due to its size, brads reduce the possibility of splitting in hardwoods. Easily
Casing: Wire nail with a slightly larger head than a finish nail. Often used for flooring and exterior door frames and trim. Tapered head can be set flush or just below work surface. Often galvanized to resist corrosion.
Shank Types, Head Styles, Thread Styles, and Point Styles
Self-drilling screws are used for quick drilling into metal and wood. The screw is easily recognized by its drill point and notched flute. Acting as a drill bit, the drill point is quicker and easier to install than switching between a drill bit and a driver bit.
Consider these key factors when selecting a self-drilling screw:
- Type and thickness of drilling material. Make sure the drilling material is softer than the screw material. If not, the screw will quickly dull and stop cutting. Determine the thickness of the material being attached so the appropriate fastener length can be selected.
- Drill Flute – An effective drill flute is responsible for clearing debris from a hole as it is being drilled. When a flute is completely embedded, it stops removing chips. When debris builds up in a hole it causes overheating, which can stop drilling.
- Point - Shape of the drilling tip
- Point Length - Determines how deeply the screw can drill
- Pilot - Must be able to completely drill through the material before the threads engage. If the threads engage before drilling is complete, the fastener can bind and break.
- Point Wings - Used on screws to fasten thicker materials, such as wood to metal. Wings drill holes larger than the threads, preventing threads from engaging the wood. When the wings hit steel, they break off, allowing the threads to engage with the steel.
How to Slow or Prevent Fastener CorrosionMetal, even stainless steel, fasteners can corrode. And, when fasteners corrode, they may lose their carrying ability. It’s important to know why corrosion happens in order to prevent or slow the process, and how to replace corroded fasteners, or if necessary, the surrounding material.
The environment where a fastener is installed is key. Ocean salt air, condensation, long-term wetness, fire retardants, fumes, fertilizers, chlorides, sulfates, preservative-treated wood, de-icing salts, construction chemicals, dissimilar metals, soils and more factors can contribute or be a direct cause of corrosion.
Structural engineers and architects should have taken such factors into account when deciding what kind of anchors and fasteners to install.