When it comes to identifying or classifying a fastener there are a number of key attributes that are used. The main attributes used in identify fasteners include fastener type(ex: drive type, head type), material(ex: stainless steel, zinc plated steel, etc), fastener diameter, length and thread count also referred to as pitch count.
Fastener Materials
There are many types of fastener types that include everything from a machine screw to carriage bolts to lag bolts and eye bolts. Each fastener type usually has specific application(s) that it is designed for although many are used universally. Head styles also greatly differ from flat head, which has a flat top with countersunk head to a hex head which has a hexagonal head, this head type is often abbreviated as HH or HX. Just like fastener types the head types are ideal in certain applications and uses and some can often be fairly universal.
Fastener Materials
Like fastener types there are various fastener materials used for specific applications. Steel is by far the most common of fastener materials which comes in various grades based on strength from Grade 2 to Alloy steel, the strongest of steel materials. Stainless steel is also very popular because of its resistance to corrosion.
In addition to steel and stainless steel fasteners there are silicone bronze also plainly called bronze, brass and aluminum fasteners, each having their own characteristics ideal for certain conditions and applications.
Fastener Diameter
When measuring the diameter of a fastener there are several different locations in which one can measure. The three most common used to measure diameters are the thread diameter, shank diameter and root diameter. Typically the thread diameter is used to determine diameter which is also known as the major diameter. Some people refer to hex bolts by the size of the head measured across the flats but this should be avoided for two primary reasons. One this can cause miscommunication and getting a larger bolt than needed and also the head size can vary.
Fastener Length
The length of a fastener and how it is measured is usually determined by the head of the fastener. Generally the length is measured from the surface to the end of the fastener, however for fasteners that have a head that site above the surface like hex bolts the measurement is from directly under the head to the end of the fastener. For fasteners like flat head screws the fastener is measured from the point on the head where the surface of the material will be to the end of the fastener.
Thread/Pitch Count
Thread or pitch count as it is also referred to is only used on fasteners that have machine thread which means they take a nut or thread into a tapped hole. The thread count simply says how fine or close together the threads of the fastener are.
In general, these 5 features are used to identify a screw. So the next time your are looking for a specific fastener or aren’t sure which is right be sure to remember the 5 ways to identify a fastener.