All About Fasteners, Chapter Two - Nuts, Bolts, and Screws

SAE Inch Nut Size Chart ISO / DIN Metric Size Nut Chart

By: This email address is being protected from spambots. You need JavaScript enabled to view it. - March 2005

In this installment of our discussion about fasteners, we'll travel into the boring but equally as critical properties of nuts and washers. We'll show you the different types of nuts that are common to our assemblies and modifications.


Nuts are probably one of the most ignored and boring types of fasteners that we use in the world of assembly, but did you know that there are many different types of nuts and each different type serves a purpose? There are machine screw nuts, hex nuts, jam nuts, nylock nuts, locking nuts, wing nuts, cap nuts, k-lock nuts, serrated flange nuts and the list goes on and on. For the purpose of this article, we'll look at a few of the most commonly used nuts, the hex nut, locking style nuts and serrated flange nuts. Here are some handy little charts from our friends at Bolt Depot.

Hex Nut

Hex Nuts

Hex nuts are the most commonly used nut in assemblies because of its versatility and wide array of sizes. Typically a hex nut has one length of engagement to its corresponding bolt. For example, if using a 1 X 20 bolt, the matching hex nut would be roughly one quarter of an inch thick to cause sufficient engagement to positively contain the fastener assembly but not over stress the bolt to cause premature failure to the assembly due to insufficient or overstretching the bolt. When combined with washers (as space permits) to evenly distribute the clamping pressure, a nut and bolt combination is a very secure way of fastening an assembly.

Nylock Nut
Locking Nut

Locking Nuts

Locking style nuts come in different styles, but the end effect is the same and that is to help lessen the opportunity of a nut loosening from the bolt under vibration laden assemblies. The "nylock" style nut uses a nylon interference washer captured on the end of the nut to help lock the nut onto the bolt and assist in capturing vibration.

The other types of locking nuts use a deformation of the thread to cause a slight interference between the nut and bolt when assembled. As this type of nut does ride the surface of the bolt, they should be used in applications of little or no frequent dis-assembly. As an assembly note, in larger sizes the amount off run on torque can be substantial and if a specific amount of torque is required, the nut should be "stepped" in to specification. By setting your torque wrench in an incremental series of 20%, 10% and final torque you can assure that the bolt and nut assembly have little to no effect from the locking mechanism of the nut.

Serrated Flange Nut

Serrated Flange Nuts

Have you ever needed a nut with a built in washer that can bite into relatively soft surfaces for some additional security in an assembly? Well then, you need a serrated flange nut. With a built in washer (actually machined or formed from the raw stock of the nut) and a series of serrations on the mating face, this nut is a perfect blend of both a locking nut and a hex nut. When used where space permits it allows high strength of full thread surface contact and a degree of vibration and impact resistance while also allowing exacting torque specifications to be achieved.

Grades and Classes / Identification

One of the more confusing areas of fastener identification is dealing with the various classifications of nuts. There are so many different types and materials; the very best way to purchase nuts is to match them to the bolt being used. This is actually made quite easy for us at our local mom and pop hardware as the bins are usually marked in common grades / classes matching the bolts. For example, a bin of Grade 8 nuts are meant for matching Grade 8 bolts and so forth. The tricky area is in specialty hardware such as high carbon content, high tensile strength bolts. This is the area where going to your local dedicated fastener store is necessary as they can help you select the absolute best matched fastener.

Future articles will focus on washers; thread locking compounds, proper application of torque and fastener use / selection for our projects.

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  • Bolt Depot
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