Nuts and Bolts about Fasteners, Chapter Two - Nuts
By: Mike Nevitt - March 2005
In this installment of our discussion about fasteners, well travel into the boring
but equally as critical properties of nuts and washers.
Well show you the different types of nuts that are common to our assemblies and modifications.
|SAE Inch Nut Size Chart
||ISO / DIN Metric Size Nut Chart
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, well 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 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 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.
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 disassembly. 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
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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