Nylon insert nuts

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Instead of lock washers, some nuts use nylon inserts to keep them on.
How many times can one put the nut on -- and off in between -- and have it still work well as a lock nut?. When does the nylon stop working?
B.
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On Sat, 04 Oct 2014 21:38:31 -0400, snipped-for-privacy@bubba.com wrote:

An engineer would say once. Every time you use it, the nylon wears and the retention is decreased.
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On Sat, 04 Oct 2014 21:38:31 -0400, snipped-for-privacy@bubba.com wrote:

That depends on the application. Some applications would possibly work fine if the nut was removed and reassembled once or maybe two times at the absolute maximum. Many applications it's a one-shot deal.
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On 10/04/2014 11:06 PM, Gordon Shumway wrote:

Long ago I encountered -- no idea where -- nuts that had a split section at the outer end -- still the same steel as the rest of the nut and perhaps threaded as well, but it grabbed the bolt tightly. Haven't seen any for a looong time. are they still used? I think the name might have been "aerolock" or "aerotight."
Perce
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On Saturday, October 4, 2014 11:29:37 PM UTC-4, Percival P. Cassidy wrote:

sounds like a type of "prevailing torque nut" - one I've seen most common is one where the threads are ovaled at one end to provide drag on the stud/bolt/screw. Not to be confused with a castellated nut which is to be used with a cotter pin.
nate
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On Saturday, October 4, 2014 10:29:37 PM UTC-5, Percival P. Cassidy wrote:

Check these: http://www.mcmaster.com/#hex-locknuts/=u0oyp6
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On 10/4/14, 9:38 PM, snipped-for-privacy@bubba.com wrote:

"Carroll Smith's Nuts, Bolts, Fasteners, and Plumbing Handbook" (1990) says the nylon isn't damaged by assembly.
The Federal Aviation Administration says it's fine to reuse them, but you should check the torque to be sure they still have the required friction.
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On 10/05/2014 12:42 AM, J Burns wrote:

+2
--


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snipped-for-privacy@bubba.com;3292289 Wrote: > Instead of lock washers, some nuts use nylon inserts to keep them on.

Well, after reading this:
'Nyloc nut - Wikipedia, the free encyclopedia' (http://en.wikipedia.org/wiki/Nyloc_nut)
I would say that Nyloc nuts can be re-used very many times without lessening the performance of the nut.
There seems to be a popular misconception about how these nuts work. People tend to think that the screw or bolt threads CUT INTO the nylon, and it's that deformation of the nylon around the screw or nut threads that prevents the nut from coming loose. This is incorrect.
Apparantly, the screw threads DO NOT cut into the nylon at all. Instead, the nylon ring stretches elastically over the screw threads. In engineering terms, elastic deformation means that the nylon returns to it's former size and shape once the force deforming it is removed. So, there is no change in the nylon ring's ID or interior surface as a result of screwing it onto a bolt or screw because all the deformation is purely elastic.
Still, that same web page says that experts disagree on this point. If'n it wuz me, I would re-use the nuts except for applications which you feel are critical and warrant the small cost of using a new nut each time.
--
nestork


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On 10/05/2014 8:40 AM, nestork wrote:

My observation over the years has been that there is some thread-cutting but it's quite minimal for quite a number of repetitions altho eventually one will begin to notice some difference in torque required if they are reused a quite large number of times. There's a filter housing on the little JD utility tractor here that uses them -- it gets checked about every 3-6 mo and is of early '90s vintage so that would have a guesstimate of some 20yr*3/yr--> ~60 cycles so far. On these I'd judge virtually no change in their characteristics to date. (They're not large, 8 mm, but I've not reason to think any others would behave much differently).
There are various other pieces of gear around that use them but no others that get frequent use as these for comparison...altho I can't recall when (or if) I've ever thought one needed replacing for having worn the nylon insert out to the point it didn't function.
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On 10/5/14, 1:05 PM, dpb wrote:

About 1983, I bought a heavy-duty string trimmer with various heads including a couple of steel blades. At least one head used a nut with a red rubbery insert. It still works fine.
I've read that an important function of an elastic insert is to maintain pressure between the nut threads and the bolt threads. Springs around carburetor screws do that, and those screws seem to stay in place regardless of vibration no matter how many times they are adjusted.
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Sounds good to me. In this case, I'll only be putting them on 3 times and there are more than one, so EVEN IF they start coming off, I'll get some warning.
Mr. Green, the problem isn't the money but the special trip to Nissan to get them. Are you like you are here in your personal life too?
And thanks, Nestork.
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On Sat, 04 Oct 2014 23:29:37 -0400, "Percival P. Cassidy"

Sometimes called "stover" nuts?likely a brand name like "kleenex".
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On Sat, 04 Oct 2014 23:29:37 -0400, "Percival P. Cassidy"

Generically known as "prevailing torque" nuts.
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On Sat, 04 Oct 2014 23:29:37 -0400, "Percival P. Cassidy"

From the website of Aspen Fasteners - a prevailing torque fastener supplier:
Description: Nylon insert torque prevailing type lock nuts contain a captive (permanent) undersized nylon (or other polymer) insert that grips the mating threads when tightened and generates the prevailing torque. The nylon insert also dampens vibration between the bolt and nut further securing the mated components and provides a gas and moisture seal. Because the threads of the mating bolt deform but do not cut into the nylon so nylon insert lock nuts may be re-used a limited number of times. These nuts are considered one-way lock nuts because they can only be installed one-way—top up. Unlike all-metal nuts, the nylon insert limits the use at elevated temperatures or when exposed to certain chemicals.
All metal prevailing torque type lock nuts achieve their prevailing torque by altering the shape of the nut in some way - most commonly by distorting the threads of the nut, which then bites into the mating part when tightened. The all-metal locking mechanism causes eventual damage to the protective coating of the threads on both bolt and nut. This increases the incidence of corrosion as well as galling. Replacing the nut will not restore the damage caused to the bolt threads. Thus there is limited re-use of all-metal lock nuts. Furthermore they are not recommended when the nut must travel down long spans of threaded shanks as the gradual wearing away of metal tends to loosen the grip of these lock nuts. All-metal lock nuts include: 1) 2-way Reversible Lock Nuts 2) Flex-Type Lock Nuts 3) Stover Lock Nuts.
According to this, "limited" re-use is allowed. I was taught that the nut must be replaced when the "prevailing torque" drops below the minimum specified torque, or when the "running torque" (basically the same as "prevailing torque" excedes a given torque (due to thread galling in the case of all metal nuts). With all metal locking nuts both the nut AND bolt can be compromised bu re-use.
There are also "fiberlok"nuts that are like nyloc but can withstand higher temperatures. Nyloc are not allowed in the engine compartment of an aircraft, for instance. Fiberloc and all-metal locknuts are, while safety wired castellated nuts are preferred.
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On Sun, 5 Oct 2014 12:41:17 +0000 (UTC), Red Green

Flex-loc nuts.

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On 10/05/2014 02:16 PM, snipped-for-privacy@snyder.on.ca wrote:

> http://www.smithfast.com/flexlocHHFHlocknuts.html
I think I've seen them, but it's not what I had in mind.
I googled the names I thought I recalled and found these:
> http://www.fastenright.com/aerotight-nuts
which are what I had in mind.

I call those castellated nuts, but they aren't what I had in mind. See above.
Perce
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wrote:

There are quite a few different tupes of "prevailing torque" nuts. Beyound the Nylock and Fiberlock type there are numerous "all metal" types which can be proken down into One-way and two-way nuts. Stovers - with a deformed thread on one end are one of the most common all-steel one-way types. Flex-locks look like a castellated nut but with slots too narrow for a cotter pin. The "castellated" prtin is displaced inward to provide the "prevailing torque" They are also one-wau locking nuts. One way locking nuts can only be installed in one orientation - locking device out.
Two way locking nuts - center-lock - have one or more indentations in the center of the "flats" of the nut, deforming the thread inward at the point(s) of indentation.. Three-bump centerlocks are the most common. They can be installed in either direction.
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On Sun, 05 Oct 2014 16:19:15 -0400, "Percival P. Cassidy"

Yea, those are a "proprietary" version of a flex-lock
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Is this what's used on factory installed lawn mower wheels?
m
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