Fastener Technical FAQ

After over 40 years in the fastener business, we've come across almost any question you could think of related to fasteners, and have had to come up with answers and solutions to them all. Common questions are listed in our FAQ below, but if you have need an answer to something not listed here, please contact us.

How do I determine the necessary torque for my application?

There is a method used to estimate the torque/tension relationship in an assembly. The Torque/Tension Equation; T = (K D P)/12 can be used to prescribe a torque value that will achieve a certain tension or clamp load. However, the best way to determine correct torque is through experimentation under actual assembly conditions. Click here to learn more.

Do fasteners need to be UL listed for use in solar applications?

The short answer is NO. General commodity commercial fasteners do not fall under the umbrella of products that would require a UL listing or ICC-ES report. As long as a bolt or fastener is manufactured to the correct ASTM, SAE, ASME, and/or AASHTO specification, there is no need for it to be tested or evaluated by ICC-ES, UL, or other similar listing services. Click here to read the full article.

What is the difference between a self-drilling screw and a self-tapping screw?

Unlike Military or Aerospace Fasteners terminology used in the Commercial Fastener Trade is often imprecise and can sometimes cause confusion, one example is the distinction between Self-Tapping and Self-Drilling Screws. A Self-Drilling Screw is a Self-Tapping Screw with the added feature of a drill point. The drill point looks a lot like the point of a drill. It will drill a hole and form the mating threads in one operation. Click here to read the full article.

Which fasteners meet my ASTM code?

The most common ASTM codes referenced for fasteners are ASTM A36, ASTM A47, ASTM A48, ASTM A153, ASTM A193, ASTM A194, ASTM A307, ASTM A320, ASTM A325, ASTM A354 and ASTM A449. Mudge is able to supply fasteners to meet these ASTM specifications and others. If you'd like to download individual ASTM standards documents, visit our Fastener ASTM Standards resource page.

What do the markings on the heads of bolts mean?

The heads of different fasteners can be stamped with a wide variety of markings onto the head. Bolt head markings usually accomplish two things: they identify both the manufacturer of the bolt and the standard to which the bolt was made. Mudge Fasteners wants to help you identify what these head markings are and when you'll need to know them. To view our full bolt head marking guide, visit our Bolt Identification Markings resource page.

Can you help me understand fastener terminology?

We know that all of the different lexicon associated with technical fastener words and phrases can be overwhelming, so we have a handy Fastener Glossary available for you to use. If you don't find what you're looking for there, just contact us for further help.

How big of pilot hole do I need for my lag screw?

Pilot or lead holes are typically used to ease the installation of lag bolts. Refer to the chart below for commonly accepted hole sizes. There are a number of variables that may change the required pilot hole dimensions including bolt length, diameter and wood species. For questions regarding specific applications, consult an engineer. To view and download our helpful Lag Screw Pilot Hole Diameter Guide, click here.

What plating does my fastener need to have?

Depending on how you're using an individual fastener, the plating or finish choice could vary between multiple options based on durability and price requirements. For more information, visit our Fastener Platings and Finishes resource page.

What are the differences in thread pitches?

Thread series cover designations of diameter/pitch combinations that are measured by the number of threads per inch (TPI) applied to a single diameter.

Coarse Thread Series (UNC/UNRC) is the most common designation for general application bolts and nuts, while Fine Thread Series (UNF/UNRF) is commonly used in precision applications. To learn more, view our Fastener Thread Pitch Charts.