Nylocks that REALLY Lock

June 14, 2020, 11:30 AM

Not sure if this should be here or the What's Your Deal section, but I'm looking for answers, not just bi+(&ing.

I got some stainless bolts and nylocks from McMaster Carr. Out of three different combinations (1/4-20, 5/16-18 and 3/8-16), only the 5/16-18 works as expected.

With the other two combinations, the nut threads freely onto the bolt until it contacts the nylon insert (2-1/2 to 3 full turns). Once it's fully into the insert (when the bolt end comes out of the nut), it seizes. Hard. Won't turn at all. Vise Grips and a socket on a breaker bar can't get it to turn. I actually had to use a Dremel cutter to remove them, and damaging (mostly cosmetic) the bracket I was trying to install.

They were ordered ~4 months apart. The 1/4-20 (seizes) and 5/16-18 (works as expected) were in the first order, and the 3/8-16 (seizes) in the second.

The 1/4-20 and 5/16-18 parts were all the same "family" (i.e., under the same section in the catalog, the same part number prefixes). One seizes, the other doesn't. (These two were Torx head; the 3/8 was carriage bolt.)

I just emailed McMaster to see what gives.

Any thoughts?

June 14, 2020, 11:49 AM

az4783054

You're on the right track by contacting McMASTER CARR first. I buy my bulk grade 8 and stainless fasteners from them in various sizes. I've never had those seize, but have had some standard stainless SAE bolts/nuts seize, as in welded solid. They don't manufacture, so it could be their source is providing out of spec Nylocks.

China maybe?

June 14, 2020, 11:58 AM

220-9er

Stainless steel nuts & bolts will gall when used without anti-seize. Has nothing to do with the anti-lock plastic part except that puts even more friction into the process of installation and removal.

https://www.atlanticfasteners....ainless-fasteners-2/

https://www.fastenal.com/conte...le%20-%20Galling.pdf

June 14, 2020, 12:02 PM

sns3guppy

If the bolts and nuts were cut correctly, galling isn't an issue, especially not in the initial installation.

To seize and require cutting can only be mismatched threads; wrong bolt, or wrong pitch for the nut.

June 14, 2020, 12:08 PM

Balzé Halzé

quote:
Originally posted by 220-9er:
Stainless steel nuts & bolts will gall when used without anti-seize. Has nothing to do with the anti-lock plastic part except that puts even more friction into the process of installation and removal.

https://www.fastenal.com/conte...le%20-%20Galling.pdf

He's saying that they are seizing up as he is threading the nut on. I've never had that happen with nylon lock nuts.

June 14, 2020, 12:27 PM

IntrepidTraveler

It's almost like they are pre-loaded with red Loctite or Superglue.

June 14, 2020, 12:39 PM

az4783054

Cut threads vs rolled threads are also a consideration. I've purchased both types and there is a definite difference in resistance when threading on a nut. I'm not certain if Nylock nuts come in rolled threads however.

I keep my fasteners in a large industrial multi compartment bin, but I have accidentally grabbed the wrong thread pitch (coarse vs fine) and that's when the stainless galled. My error for not checking more carefully.

Are you certain you didn't use a metric on SAE or the opposite?

June 14, 2020, 12:53 PM

Balzé Halzé

quote:
Originally posted by az4783054:

Are you certain you didn't use a metric on SAE or the opposite?

That's a good thought. Although it likely would've binded long before the threads stuck out of the nut.

June 14, 2020, 12:59 PM

jimmy123x

quote:
Originally posted by 220-9er:
Stainless steel nuts & bolts will gall when used without anti-seize. Has nothing to do with the anti-lock plastic part except that puts even more friction into the process of installation and removal.

https://www.atlanticfasteners....ainless-fasteners-2/

https://www.fastenal.com/conte...le%20-%20Galling.pdf

STainless steel nuts and bolts don't generally gall when using hand tools or ever. I work with stainless nuts and bolts ALL of the time. Maybe if you ran a nut down 5" of threads with an impact wrench, but galling generally does not happen.

It sounds to me like either the nuts or bolts are the wrong thread...... there's 1/4" fine thread 1/4"x28 and regular 1/4"x20. They could've also accidentally sold you nuts or bolts where one of them is a close metric size.

June 14, 2020, 01:09 PM

IntrepidTraveler

Well, they came straight out of the boxes that McMaster shipped to me, and were marked correctly. Again, they did (do, for the ones I have left) spin on easily up to the point of contact with the nylon.

I ordered all the same thread sizes/ pitches, and the boxes match what I ordered.

June 14, 2020, 01:27 PM

shiftyvtec

Maybe they over staked (crimped) the thin section that retains the nylon locking section that's galling during make-up?

Maybe pry the nylon out of a new nut and see if the nut will freely thread.

June 14, 2020, 01:42 PM

cparktd

I think I would try running a tap through them and see what that does.

June 14, 2020, 01:48 PM

46and2

I bet it's the wrong thread pitch.

So easy to mess up in packaging and whatnot.

Seen it tons.

June 14, 2020, 02:02 PM

XLT

I had the same exact thing happen to me putting my boat together, the next set I purchased I put a drop of oil on them and they all worked fine I thinking that they some how caught a thread and stated galling. it really surprised me being they were all brand new with the first time using them.

I had to snap them off to remove them.

many years ago I was installing a bow eye on a huge boat I had to crawl down into a hole just to get there and no way to turn the nut with a wrench so My buddy hands me a butterfly air wrench the nut got hot seize up and it took a day to remove it what a pain in the ass I will never forget and never use an impact on stainless again. the bow eye cost about 100 bucks for the first one.

June 15, 2020, 01:00 PM

IntrepidTraveler

Well, McMaster replied. from their explanation, the only one that applies would be galling. The fasteners were new and in good condition, I installed with hand tools, not too quickly, and the parts were flush when installing. So I ordered some anti-seize, and will try that.

Here is their reply:

quote:

There are a couple of issues that could be causing the bolts and nuts that you purchased to seize.

First, nylon insert locknuts are designed to be difficult to thread on once you reach the nylon insert. If you're trying to thread them on by hand, it's going to be very difficult to get them on and off. They are reusable, but still difficult to remove due to the locking nature of the nut.

The other, and more likely, issue is that, since these are stainless steel fasteners, you could be experiencing thread galling, which is where pressure and friction cause bolt threads to seize during installation. There are several steps you can take to help you avoid thread galling:

1. Slow down the installation speed. It is recommended to not use power tools when installing stainless steel fasteners to help avoid galling.

2. Don't use bolts to pull joints together. If the pieces that need to be bolted together don't stay together well, using a vise or clamp is better than trying to use the bolts to pull them together.

3. Try using a thread lubricant, like those we sell here.

4. Check the threads prior to use for damaged or dirty threads. If you notice any dirt or damage, don't use those fasteners.

5. If the fastener begins to bind, stop tightening it. Wait a couple of minutes for heat to dissipate before resuming installation. Since you're using locknuts, this will be more of an issue as the nylon insert creates more friction, and thus heat, during installation that can make thread galling more likely.

June 15, 2020, 02:19 PM

220-9er

quote:
Originally posted by Mustang-PaPa:
220-9er is correct IMO. I have used a lot of SS in the food industry and SS galling is an issue. Anti-seize is a used alot.

If I were to take a guess at what is causing your galling issue its the nylock itself. When the bolt contacts the nylock its causing the threads to gall from the resistance of the bolt trying to push through it.
Grease/oil will work in a pinch. Try lubing up the problem bolts and nuts and see if it doesn't help with your issue.

It's basic metallurgy and I discovered this particular problem by accident myself, not because of some great wisdom or depth of knowledge (that I didn't have at the time). So I looked it up.
I did know that lots of high hardness and high wear potential applications like older cams and tappets have to have a slightly different hardness so one part can wear, even if it's very slight, or the two parts will fail together.
Stainless isn't a particularly hard type of steel but it has an almost "sticky" property against the exact same material and also has lots of microscopic burrs when the threads are cut that tend to catch on each other. That's why it can be tricky stuff to just drill a hole through and break drill bits.
I guess the nylock gives just enough drag to cause enough friction to help make this happen. It doesn't seem to happen unless the threaded area is long enough. In other words if the bolt length is just long enough that the threads just stick out past the Nylock when tight, it doesn't seem to be a problem. Also a nut without nylock usually isn't a problem either.
If my explanation doesn't make sense (my wife often tells me that about just about everything else) you can look it up for a better version.