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Old 01-29-2012, 08:24 AM   #1
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Tight bolt threads by design??


man, some threaded studs have the tightest nuts when unscrewing, seems like they were designed that way. Whats the deal?? I mean, say youre normally expecting to loosen the nut with a wrench and after say, one turn, if the threads are clean, you expect to unscrew the rest of the way just with your fingers, right? But geez, some nuts, perhaps enginered for the more critical car parts (brackets, etc) will no way "spin" off. They need continual force applied to unscrew with a clumsy open end wrench/deep socket.

has anyone noticed this? I am tempted to buy a new nut that spins off freely. Dont understand. This one nut has to be unscrewede on your backk, under the car, looking toward the sky. Soooooo tedious.

Thanks

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Old 01-29-2012, 08:58 AM   #2
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Tight bolt threads by design??


OK, just did something- I measured with a caliper, the diameter of that nut and found out that one side (one hex to the opposite hex) is NARROWER than the other 2 "hex" diameters!! I never knew this!! Was this nut designed that way? Or did it warp'mutate over the years? How can a nut warp?? Also, revelation- I threaded this nut onto another similar size bolt and it threads nicely to about say, 80% of the distance then tightens up so badly. Again, design?

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Old 01-29-2012, 09:51 AM   #3
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Tight bolt threads by design??


Nuts and bolts are produced in a variety of ways, with threads formed(rolled) or cut. There are also different 'fit' criteria, some are made to fit tightly, some a little looserThey are made in mass runs of thousands of pieces. Even with the most stringent QC in place, a few bad ones can slip through. Though the outside dimensions of the nut shouldn't have anything to do with the bore and thread dimensions, it is possible that the hex stock was not perfect, allowing the hole to be drilled and threaded off center or skewed as it passed through the screw machine.
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Old 01-29-2012, 10:11 AM   #4
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Tight bolt threads by design??


You state that the distance across one set of "flats" on the nut are smaller than the others, but by how much? It would not be unusual for this distance to be off by .010" (ten thousands of an inch) and be within manufacturers specs. NOW--some nuts are "mal-formed" at the factory so as to make them tight on the male screw part. This is to keep the nut from backing off during normal use. Look carefully at the nut you have, does it have any indentations on any of the flats or multiple flats? This would be a sign of intentional deformation. Also look at one side of the but to see if either side looks to be "mal-formed" this is also a way some manufacturers make their nuts to be tight when screwed on. The general rule of thumb in industrial applications is that if you remove one of these type "lock-nuts" you discard it and use a new one. This would also apply to the "lock-nut's" with the plastic put into the side of the nut. BUT--the nuts with the plastic made into one end of the nut is different. These are a true "vibration resistant" type nut and may be used multiple times, but not many. Too cheap to use a new nut in this type application. Being as you stated "on your back, under the car", what was this nut holding up/on?
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Old 01-29-2012, 11:04 AM   #5
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Tight bolt threads by design??


yes, I do agree. just FYI, I can compare to philosophies on fitment - one from the USSR, where I worked as a tool make, and one here, in the USA. last meaning - Asian and European makes also. ALL bolt holes back in the ol' country where countersunk and threads had somewhat higher tolerance. as a result, it was much easier to guide a bolt into its hole. I do not remember seeing any countersunk holes here. and all you do is kuss and try to fit that bolt in just right, or it won't go. wild guess - "costs more" to countersink?
next observation - threads mating here has fractional tolerances. which I understand, it's PRECISION, but that precision bites you in your ars oh so much down the road. just like quacks mentioned. I currently work as a prosthetist, and we have to deal with this all the time on mechanical components. I call it over engineering.
next observation is - they came up with gazillion of various self locking/tightening nuts here. regular locking washer is not good enought. you have to have nylon washer nuts, self toghtening nts, pinch nuts, you name. I donno if lawyers had their fingers in this, or it's perversely made that way on purpose, just to scare tree shade mechs away from working on their cars, and give more butter to dealers bread, or what.
all I can say is - if you have over engineered precision, mixed on use of cheap metals, like GM does, you screwed many times over, as their bolts either don't budge at all, or snap, or heads strip in a heartbeat.
that's just opinion of a tree shade mech DIY or die guy. oh, yeah, and you just start me of German and Swedish ingenuity....
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Old 01-29-2012, 02:12 PM   #6
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Tight bolt threads by design??


Yes, thread interference is a common way to prevent fasteners from loosening and it works well. It can be on an internal thread or external.

<----- fastener engineer for 14 years
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Old 01-29-2012, 03:10 PM   #7
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Tight bolt threads by design??


Stoverized” lock nut

“This means that the top of the nut has been slightly reshaped to deform the inner threaded section. It works similar to the more obvious and familiar 'nylock' nut,with the nylon insert.”

http://www.merkurtech.com/merkurtech/techarticles/item029.php
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Old 01-29-2012, 05:18 PM   #8
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Tight bolt threads by design??


Thaats right, you guys!!! (sorry for late reply). yes, the difference is so slight- maybe 1mm or so only, but enough to make the end tighter when screwed on! I meanwhile searched around and found some call them "crimped head" nut (?). Would that make sense?

Geez, Im both hapopt and mad- happy cuz I learned something and you people confirmed these nuts are normal/made that way for specific reason, and MAD cuz I now understand I should NOT replace them with un crimped/deformed ones just so I can spin them on easier/quicker. Guess my alternator/power steering pump bracket need those tight "critical" nuts tight like that to prevent loosening under heavy vibration/use. (soooo hard to thread them on- sheesh, under car/upside down, with only open end wrench).
Thaks, People.
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Old 01-29-2012, 05:21 PM   #9
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Tight bolt threads by design??


Quote:
Originally Posted by Thurman View Post
You state that the distance across one set of "flats" on the nut are smaller than the others, but by how much? It would not be unusual for this distance to be off by .010" (ten thousands of an inch) and be within manufacturers specs. NOW--some nuts are "mal-formed" at the factory so as to make them tight on the male screw part. This is to keep the nut from backing off during normal use. Look carefully at the nut you have, does it have any indentations on any of the flats or multiple flats? This would be a sign of intentional deformation. Also look at one side of the but to see if either side looks to be "mal-formed" this is also a way some manufacturers make their nuts to be tight when screwed on. The general rule of thumb in industrial applications is that if you remove one of these type "lock-nuts" you discard it and use a new one. This would also apply to the "lock-nut's" with the plastic put into the side of the nut. BUT--the nuts with the plastic made into one end of the nut is different. These are a true "vibration resistant" type nut and may be used multiple times, but not many. Too cheap to use a new nut in this type application. Being as you stated "on your back, under the car", what was this nut holding up/on?
This nut goes on the studs (2 of them) that hold a big aluminum bracket which mounts both alt and PSP. Yes, it clearly shows that "malformed indentation/squashed look. Thanks, Thur.
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Old 01-29-2012, 05:38 PM   #10
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Tight bolt threads by design??


If the nut goes on easy then it needs to be replaced. I will bet that there was no lock washer either.
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Old 01-29-2012, 05:52 PM   #11
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Tight bolt threads by design??


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If the nut goes on easy then it needs to be replaced. I will bet that there was no lock washer either.
Dont worry, hardaway, that nut NEVER went on easy......LOL. Ive done this a bunch of times, and its always a big PAIN! Nut threads on easy only at first- say, 2/3 to 3/4 of the way the distance to bolt protrusion then man, it tightens up!! Its still a "good" nut, I think.

Right, no lock washer. Wouldnt the lock washer do the same job?? Just seems there could be a better way.........
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Old 01-29-2012, 05:54 PM   #12
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Tight bolt threads by design??


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Dont worry, hardaway, that nut NEVER went on easy......LOL. Ive done this a bunch of times, and its always a big PAIN! Nut threads on easy only at first- say, 2/3 to 3/4 of the way the distance to bolt protrusion then man, it tightens up!! Its still a "good" nut, I think.

Right, no lock washer. Wouldnt the lock washer do the same job?? Just seems there could be a better way.........
The nut is good.
Used to be standard nut with a lock washer. One less thing to put on and pennies add up.
Tip of the day, if you ever need a lock nut in a pinch. Just set standard nut on its side on hard surface and tap it with a hammer just enough to slightly out of round. Then you have a lock nut.

Last edited by Hardway; 01-29-2012 at 06:00 PM.
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Old 01-29-2012, 06:07 PM   #13
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Tight bolt threads by design??


Hardaway, are you saying for sure, one can substitute a lock nut washer and a easy to spin on nut for this dang hard nut?? That they did this only to save 4 cents? Same effectiveness? If so, Im happy! Might even put on red loctite- anything- PLEEEEEEEAsE to avoid putting that back on.
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Old 01-29-2012, 06:10 PM   #14
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Hardaway, are you saying for sure, one can substitute a lock nut washer and a easy to spin on nut for this dang hard nut?? That they did this only to save 4 cents? Same effectiveness? If so, Im happy! Might even put on red loctite- anything- PLEEEEEEEAsE to avoid putting that back on.
no i am not saying that or sugesting that.
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Old 01-29-2012, 06:25 PM   #15
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Tight bolt threads by design??


OK, thanks. Just wanted to be sure if that wood be OK. I'll stick with factory then. No chances.

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