FTM 154: ASME B18.16.6 nylon insert lock nuts

ASME B18.16.6 covers both Nylon Insert Lock Nuts and All Metal Lock nuts of the prevailing torque type

This edition of the Fastener Training Minute with Carmen Vertullo was originally published July 21, 2020 as “ASME B18.16.6 nylon insert lock nuts” during episode 154 of Fully Threaded Radio.

Today’s topic, like many of our topics came via an email question. Actually, it was a problem that a client had regarding the proper designation of nylon insert lock nuts. And there is a rather interesting and a little complicated way that nylon insert and all prevailing torque nuts are designated out of a standard called ASME B18.16.6.

ASME B18.16.6 covers both nylon insert lock nuts and all metal lock nuts of the prevailing torque type. Prevailing torque means that they don’t spin on by hand. You have to give him a little bit of a wrench help to get them past whatever the Locking element is. We are very often referring to these lock nuts incorrectly. I had a drawing that came my way recently and the drawing indicated that it was a nylon insert lock nut and they called it a Grade C. That was incorrect and we’re going to explain to you why that was incorrect.

But first, let’s maybe cover the basics of be B18.16.6. ASME B18.6.6 is a fairly full-featured standard. It covers both the dimensional and the performance requirements of nylon insert lock nuts and all metal lock nuts and it has a very good designation system for both the dimensions of nylon insert lock nuts and the performance of both nylon insert lock nuts and all metal lock nuts.

Let’s start with nylon insert lock nuts. They come in different styles, styles meaning the size and shape of the lock nut and probably the most common nylon insert lock nut style is called the “NE”, and those go from 1/4 inch up to 1 1/2 inches in size. It is a regular hex nut shape, nothing special about it. Then there is the next one which is similar to the “NE”, but it’s thinner and like a jam nut, and it’s called style “NTE”. Whenever you see a “T” in the designation, it means “thin”. It also goes from 1/4 inch to 1 1/2 inches.

In the larger lock nuts we have a style called “NU” that’s like a heavy hex nut. It has a larger width across the flats, and those go from 1/4 inch up to 3 inches in size. There’s a thin version of that and it’s called an “NTU” as you would expect. The thin “NTU” type nut or Heavy hex Nut also goes from a 1/4 inch to 3 inches.

So those are the sizes that we would use with bolts. When we get down into screws, we have a designation called “NM”. Style “NM” is from size number two up to size number 12 (#2 to #12), and it’s for use with machine screws. So when you think of “NM”, the “M” is for machine screw. There’s also a thin version of that and it’s called the “NTM” in that would be like a machine screw jam nut.

So, “NE”, “NTE”, “NU”, “NTU”, “NM”, and “NTM” are the different types of nylon insert lock nuts as designated by their dimensions. Beyond that, of course, we have to designate them in terms of their performance.

In the nylon insert lock nut world, the performance is designated with the letter “N”. Either an “N2”, an “N5”, or an “N8”, just like grades 2, 5 and 8. So the “N2” nylon insert lock nut is a Grade 2, the “N5” is like a Grade 5, and the “N8” is like a Grade 8. So if we were to properly designate a grade 5 nylon insert lock nut, we would say “N5”.

When we go into all metal lock nuts, we don’t have any of those designations regarding Dimensions, though there is a table for dimensions. But there’s only one all metal lock nut, there’s no thin versions or heavy hex versions in the standard. But they have similar grades, and those grades are Grade A, Grade B, and Grade C, which would follow Grades 2, 5, 8. Grade A being Grade 2, Grade B being Grade 5, and Grade C being Grade 8.

And then additionally we have two other types of nuts and these would be our flange nuts. And those are Grades “F” and “G” in either a nylon insert lock nut or an all metal lock with a flange. The “F” Grade is like a Grade 5 or Grade B. And the “G” is like a Grade 8 or Grade C. So that is how we designate properly nylon insert lock nuts from ASME B18.16.6. It’s in your IFI book, so I would recommend that you get it out and read it if you’re selling or using lots of nylon insert lock nuts. It’s an excellent specification to learn about: its full-featured, and it covers all the dimensional and performance requirements of these nylon insert lock nuts.

By the way, there is no provision for any other material in the standard except for carbon steel. So all of these nuts are made from carbon steel. It does say that you can make them out of whatever material that you want, provided that the performance requirements are agreed upon between the customer and the seller. So you can make them out of stainless steel, you can make them out of brass or aluminum, and they often are made out of other materials, but the standard does not cover those materials.

Well, I hope that helps you know more about how to properly designate prevailing torque lock nuts from ASME B18.16.6.

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