Ubolt Question

kito · Mar 28, 2016

As long as you are getting the full thread length of your nut. I always use Nylock nuts instead of split washers and have the stud stick out far enough to hold an acorn nut for aesthetic purposes if not hidden.

centerline · Mar 28, 2016

The threaded rod/bolt only needs 1 thread length past the nut to insure full holding strength of the nut

kito · Mar 28, 2016

Depends on the thread size and pitch plus what grade fastener you are using. There should be tables available online somewhere for recommended torque values. Also, if using Nylocks, those values should be considered above the running torque.

Capt jgw · Mar 28, 2016

Just google "torque values". You'll get many hits for charts that for the most part agree.

centerline · Mar 28, 2016

Im assuming the U-bolt is stainless, so if the nut is stainless also make sure you have either a marine grade never-seize (I prefer the nickle type never-seize) or some lanacote on the threads or when you approach the torque values it has a high chance of galling the threads, which is a bad and usually permanent situation....

JamesG161 · Mar 28, 2016

centerline said:
The threaded rod/bolt only needs 1 thread length past the nut to insure full holding strength of the nut

This good practice to verify the minimum design tensile load of the bolt (visually), but only 3 engaged threads are required. A drop of Loctite Blue works too, if you want to eliminate the lock washer of the same metal as the bolt.
Jim...

Capt jgw · Mar 29, 2016

The bolt does not need to extend past the nut at all. You can even grind it flush of you want to. The PO of my boat never did that and everything he mounted had one or two inches of bolt sticking out with an acorn nut on the end as a "cushion". Acorn nut or not, you bump your head on one and it hurts like hell. I spent a whole day with my Dremel grinding those things off.

centerline · Mar 29, 2016

JamesG161 said:
This good practice to verify the minimum design tensile load of the bolt (visually), but only 3 engaged threads are required. A drop of Loctite Blue works too, if you want to eliminate the lock washer of the same metal as the bolt.
Jim...

I will disagree, only because if you have just 3 threads of the nut engaged on the bolt, you have lost the potential holding power of the remaining threads that are not being used.... so you have lost a lot of the holding power of nut.

but.... if we are only talking torque specs here, we might come to an agreement that 3 threads could be sufficient to meet them, but the very minimum without room for excess is a high stakes gamble where you have everything to lose and absolutely nothing to gain...
and as much as I believe in following torque spec's, some of us know that nuts/bolts commonly get very much greater loads put on them than what the torque spec does. so in the real world, more material holding the fastening will be better and more reliable than the very minimum needed to meet torque specs...

and one thread past the nut.... if you look at the end of a bolt as it comes thru a nut, you will see it has a very slight taper to it... this allows ease in getting the nut started on the bolt. once the taper is past the end of the nut, it will have its full holding potential, and not until...... and then the taper/excess bolt can be cut off and still maintain fully engaged threads....

in my job, I commonly pull threaded nuts/bolts to failure... not on purpose, but just because the pressures get so extreme sometimes that the threads will fail..... by putting several nuts on a threaded bolt/rod, the holding power is much greater, to the point where the bolt will be pulled in two....
having only three threads engaged will allow the complete and sudden failure when the threads pull, but having excess threads past the nut, will allow the immediate threads to pull, but a little more pressure is required to continue pulling the nut off of the remaining threads...

tgrady · Mar 29, 2016

Three threads are all you need for strength. But I wouldn't fly on a vehicle on water, air of land with that type of sloppy workmanship. Vibration will still get you. Flush is good.

Tata duende · Mar 30, 2016

Consider that the tension on the rigging will change every time you tack so the fitting will tend to work just a little bit and create a situation that will tend to loosen the nuts. I would let the threads extend a little and use the nylock nuts and/or double nuts along with fender washers if you can fit them. Also check them for tightness after the first couple of outings and then periodically. The extended thread will not add to strength, but will be a safety factor in case the nuts do start to loosen over time.

Dennis Kitchen · Apr 14, 2016

Wesleysherman said "When installed with the SS Washer and locking washer there is only approx 1/8" of the bolt protruding from the nut." Guys,
Threads sticking out past the nut aren't doing anything. They are not adding strength; they are just hanging in the air. The reason for having a number of threads protrude past the nut is to (1- insure the last thread is in fact fully engaged and (2- have a little safety margin if the nut begins to loosen so that you might have the time and opportunity to re-tighten it before it falls off.
In the aircraft industry 3 exposed threads is the standard, that along with friction lock nuts or safety wire. Your 1/8 inch won't make 3 threads but in your application I'd say it is perfectly acceptable.
Again, exposed threads hanging out into the air can not make it stronger. It is "convention" so at a glance a fastener can be determined to meet minimum conformity for safety margin.

Dennis Kitchen · Apr 14, 2016

wesleysherman said:
That is actually a good idea, as it would eliminate the lock washer giving me a bit more exposed thread!
anyone know other than SS Nut is there a grade that one should look for, quality strength wise!

Thank you

Most SS hardware is type 304, otherwise known as 18-8 . While not as corrosion resistant as 316 it is stronger, therefore usually the standard. Avoid any of the "free machining" type 303 as it is much weaker and less corrosion resistant.
On another note, when replacing highly loaded rigging fittings be sure you are using "formed" or "forged" not investment cast as the tensile strength is much less in the later.

Ubolt Question

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SBO Weather and Forecasting Forum Jim & John

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