How many threads past the nut?

[bluedog225]

I’m doubting myself. Is it three threads past the nut for full strength? Thanks

 

[LeeG]

Thread Engagement - Portland Bolt

How much thread engagement is recommended, i.e. how many threads should extend beyond the nut?

www.portlandbolt.com

I figure once the nut threads are fully engaged, you‘re set.

Lee

 

[larry_g]

I’m doubting myself. Is it three threads past the nut for full strength? Thanks

Never heard such a thing. Threads past the nut add nothing to the holding strength.

 

[Leaflessshadetree]

I'd say at least 1 (2 or 3 is better). Some bolts/screws the first threads aren't full diameter.

 

[Spud McGee]

Never heard such a thing. Threads past the nut add nothing to the holding strength.

I think the extra threads could offer some level of backup in case the nut rattles loose or something?

 

[bluedog225]

Good info. Thanks

I think younger me researched it and decided 3 was a good safe harbor.

 

[alwaysFlOoReD]

2 threads where I work.
Converting semi-trucks into RV haulers.

 

[kbeefy]

2 threads. Bolts stretch under load, you need a little meat past the last thread for maximum strength.

 

[Jim greengo]

2 threads. Bolts stretch under load, you need a little meat past the last thread for maximum strength.

Depends onthe kind/grade of bolt,some bolts don't like being stretched.

 

[Paycheck]

USAF taught me 3.

 

[nadogail]

I was taught at least one thread, but no more than three.

 

[kwb]

Our standard at work is minimum of 2.

Not getting you anything for strength but it sure does make it a lot easier to get things started when the bolts are going to draw things together.

 

[Rusted Nut]

The standard as I have always know it is; minimum two full threads for most stuff, but does vary with bolt types/strengths/etc… Large nut/bolts (like large pipe restrains, mega lugs, and street lights) I have minimum four threads.

 

[Mikeske]

USAF taught me 3.

Same here and Boeing requires 3 threads also in all applications. I know that as I spent 30 years at Boeing and that was always the way they did it.

 

[ycgoat]

My understanding past the nut starts to have a maximum length before it becomes an impalement hazard that needs to be fixed by cutting it off or covered

 

[ZRX61]

Same here and Boeing requires 3 threads also in all applications. I know that as I spent 30 years at Boeing and that was always the way they did it.

FAA calls for 1 1/2

 

[bluedog225]

Deleted

 

[olytdi]

I'd like to see the engineering proof that any threads past the point of capture by a nut influences anything beside being able to confirm that the bolt is full thread bearing and not recessed into the nut.

 

[Ole Slewfoot]

Depends onthe kind/grade of bolt,some bolts don't like being stretched.

All of them stretch,.some tolerate that better than others.

Never heard such a thing. Threads past the nut add nothing to the holding strength.

We've paid for exhaustive research on the topic with this conclusion.


MSFC-STD-486B

 

[MattGarage]

I'd be concerned about shear forces, dynamic forces, play, bolt grade, type of locking (sealant/rubber/lock washer/etc) and other factors. Not enough info provided in my view and as mentioned.

 

[jayemm]

Going back over 40 years, I remember learning that 3 full threads engaged developed the full strength of the fastener(bolt).

 

[Adaylate]

If I remember correctly. International Car Show standard is 1 and 1/2.

 

[Jim greengo]

All of them stretch,.some tolerate that better than others.


We've paid for exhaustive research on the topic with this conclusion.


MSFC-STD-486B

It's the part where things snap off and going flying after the bolt gives that I'm concerned about.
Especially with harder grade bolts.

 

[TheLawnRanger]

I've seen several iffy threads get past the moderators.

 

[finn]

Depends onthe kind/grade of bolt,some bolts don't like being stretched.

Bolt clamp load is the result of stretch. Without stretch and spring rate, you have no clamp load.

 

[Jim greengo]

Bolt clamp load is the result of stretch. Without stretch and spring rate, you have no clamp load.

How often does that come into playing the average project?
If you want to measure every bolt you install for stretch,have at it.
I'll save it for special occasions myself.
Meanwhile I'll put my faith in lock washers for the majority of things.
I've built/driven/ridden some really fast/powerful machines over the years built using loc tite,lock washers and torque wrenches.

 

[finn]

How often does that come into playing the average project?
If you want to measure every bolt you install for stretch,have at it.
I'll save it for special occasions myself.
Meanwhile I'll put my faith in lock washers for the majority of things.
I've built/driven/ridden some really fast/powerful machines over the years built using loc tite,lock washers and torque wrenches.

You don’t need a stretch gauge. Thats just how bolted joints work. The joint designer understands that. The farmer or mechanic likely doesn’t, through no fault of their own.

Lock washers fell out of favor for critical joints fifty or more years ago. They’ve relics, used where the designer doesn’t really understand how bolted joints work.

How many lock washers do Cat and Deere, for example, use in the construction of modern products?

 

[laser3kw]

I was taught that the first thread and a half are not "fully formed" and should not be relied on for strength of the joint. This includes self locking and nylon collard nuts.

 

[4 FN 27]

All of them stretch,.some tolerate that better than others.


We've paid for exhaustive research on the topic with this conclusion.


MSFC-STD-486B

Doing the math, basically 2 Threads on all Thread Pitches. That is what we used building Race Cars.

 

[kaymccampbell]

I was taught 3.

 

[NUTTSGT]

Doing the math, basically 2 Threads on all Thread Pitches. That is what we used building Race Cars.

NHRA say 3 for lug nuts ?

 

[Snip]

Going three gives you enough meat to place a small bead of weld on it and make it a "locknut". Lol. Really though as long as I have at lease 2 showing I feel comfortable, as one poster said the first thread may not be a full diameter.

 

[4 FN 27]

NHRA say 3 for lug nuts ?

Good point, Lug Nuts are the exception. Per the rules:

 

[andyvh1959]

Extra length/extra threads may help assembly, getting locking devices onto the fastener. Isn't all the talk of "stretch" only applicable within the loaded length of the fastener? Threads beyond the stack of fastener, locking devices and surfaces held together don't add any strength. But is seems the "standard" is 1-1/2 to 3 threads.

 

[bwringer]

I'd like to see the engineering proof that any threads past the point of capture by a nut influences anything beside being able to confirm that the bolt is full thread bearing and not recessed into the nut.

Right, threads sticking out into thin air don't add any holding power. It's only for visual confirmation of full engagement. And in some applications with multiple fasteners, threads sticking out is a confirmation that engagement and torque are roughly the same all around.

In applications where torquing compresses a gasket, crush sleeve, packing or whatever, obviously you need some extra threads.

 

[ntsqd]

Counting threads isn't easy, where exactly do you start? I've long used the "One Fastener Diameter" rule. I can eyeball that easily, even from a distance, and where I start measuring is simple to determine. Few of my assemblies are raced and none of them are being launched into space or even into the air so the small difference in weight of each bolted assembly isn't important.

+Eleventeen on not using lockwashers. Read Carroll Smith's "Engineer to Win" for a thorough explanation about why lockwashers are the Evil Incarnate. OK, well maybe not quite that bad, but they're bad. Read the book anyway. While you're at it pick that same author's "Nuts, Bolts, Fasteners, and Plumbing".

 

[RoninB4]

Just a thought here. Nuts can be of varying thickness (jam nuts, nylock nuts, castle nuts, etc.) for several reasons so the number of threads past the nut doesn't sounds like a very consistent standard unless (hold your laughter) your nuts are consistent. In the machine tool industry we used 1-1/2 times the diameter of the bolt/screw for thread engagement for a quick rule of thumb. Perhaps just 1 X the minor thread diameter (or perhaps even the thread pitch diameter) is sufficient but we used 1-1/2 times the major diameter because it was easier to quickly calculate and eliminated any partial formed threads or c'sinking.

 

[dchawk81]

I've seen several iffy threads get past the moderators.

Are you saying the moderators are nuts?

 

[laser3kw]

a thorough explanation about why lock washers are the Evil Incarnate.

don't get started on lock washers. That is equivalent to PVC air lines, oil filters.....

 

[Bill T]

Most standards specify full thread engagement. Obviously, the more engagement you have, the more likely the optimal strength of the fastener is met. Each thread that is engaged, the stronger the threaded joint is .The strength of joint is dependant upon the fastener material, the size of the fastener and the method of torque/tensioning. To qualify a joint in a design, the
Engineer assumes all threads are engaged.
I work in the nuclear industry. Most of our current standards just specify a "full-nut". As a number of fasteners have a tapered lead, some specs/codes will specify one or two threads must extend past the nut to ensure full thread engagements.