bolt, screw, or rivet?

[inarathree]

How do I know when to use a bolt (either nut/bolt, or drill and tap), self tapping screw (or regular screw) or use a pop rivet to attach something?

I was thinking of this as I am adding a cheek block and pad eye to my boom for reefing. I could drill and use a nut and bolt, a self tapping screw, or use a pop rivet. In this case, I have only seen these items riveted to the boom

Just wondering.

 

[Griffinroydonald]

I have used self tapping screws on the boom with bad results. They would work loose and fall out. I would try the rivets to hold your parts to the boom. I have used a bolt to secure the bale on the boom for the Boom Vang with good results.

 

[Steve Dion]

I would also think that rivets would be your best bet. Of course if you have access to the back side to use a nut there is nothing wrong with that either. Just remember because you can get the nut on the bolt, does NOT necessarily mean you will be able to easily get them off.

 

[centerline]

as Griffinroydonald points out, self tapping screws are a bad idea on the boom, and i will add, they are a bad idea anywhere else on a boat.

self tappers, as opposed to regular stainless screws, will cut away too much material as it self taps its way thru your project, leaving too little holding power to be secure for any length of time.
regular stainless screws can work well if you don't over drill your hole and use something like lanocote to lube the screw as you install it.... and you want it tight but you don't want to over tighten it as you can pull the threads leaving you with a stripped hole....
the lanocote will lube the screw as its drives itself thru the high friction aluminum and it will help prevent corrosion from starting between the aluminum and stainless.

but for your purposes and longevity in the salt atmosphere, I think the pop rivets would be the way you should go.

but even with the pop rivets it would be good to lightly dip the rivets in lanocote before inserting in the hole, as this will give a bit of lubrication when the rivets are seating as you "pop" them, making for a tighter connection....

 

[captanthony]

You could also use a rivet nut, it's just like a rivet. You install the rivet nut and then can use a bolt to attach the block. They are stronger and will hold up longer. Here is a link to one, if you have never seen one before. It's the plier style. Good luck.
http://www.mcmaster.com/#rivet-nut-installation-tools/=ljyofk

 

[Bill Roosa]

You use a bolt and nut when you have access to the nut once the part is assembled.
I've used MACHINE screws and a tap with great results on aluminum. You do have to coat the SS screw threads with "never seize" before the install to keep them from reacting to the aluminum though.
Self taping screws are used for sheet metal not structural parts. As another poster mentioned they fall out after a time due to their threads being cut on a cone and not a cylinder.
SS pop rivets have the same problem as SS screws so use aluminum ones on aluminum parts. The SS rivets need a special machine to install anyway so ...... An aluminum pop rivet machine will do about 3 SS rivets before it goes south however.
the problem with pop rivets is you have to get the size right. they are made to attach a certain thickness of material so to short or to long a rivet will not "squish down" correctly and the part will either fall off immediately or be loose and fall off after it works the rivet through (probably at the worst time)

 

[captanthony]

While still using the never seize to coat the threads to break them apart, I would'nt rely on that just to stop the corrosion. I have had excellent results with these nylon shoulder washers,(the flanged with headed sleeves) and you can use a stainless fastener with these!
http://www.mcmaster.com/#sleeve-washers/=ljywqe
I used these on my canvas button snaps, which have a stainless machine screw that passes through the aluminum, and isolated that screw with these and haven't seen corrosion around the paint under the washers since. Rivet nuts work really well and can hold alot of weight, I once used them onboard commercial boats that held benches to aluminum decks.

 

[centerline]

While still using the never seize to coat the threads to break them apart, I would'nt rely on that just to stop the corrosion. I have had excellent results with these nylon shoulder washers,(the flanged with headed sleeves) and you can use a stainless fastener with these!
http://www.mcmaster.com/#sleeve-washers/=ljywqe
I used these on my canvas button snaps, which have a stainless machine screw that passes through the aluminum, and isolated that screw with these and haven't seen corrosion around the paint under the washers since. Rivet nuts work really well and can hold alot of weight, I once used them onboard commercial boats that held benches to aluminum decks.

the riv-nuts are extremely strong for some things, but they are basically a pop rivet with threads......they can be steel or aluminum, so what happens is, when the corrosion or dried salt gets in the threads and you want to remove the fastener, it will spin the rivit in the hole but the threads wont come free.... so your stuck with a loose fastener in an oversized hole... and absolutely nothing you can do about it except tear it out, weld up the hole, install the correct fastner and learn that riv-nuts have their uses, but they are limited, and mostly by people who are paying someone else to install them, so the project can be finished quickly and sold to an unsuspecting customer.... as in "the make-a-buck-pass-the-problem program" so many manufactures operate under these days...:cry:

 

[captanthony]

Again, Rivnuts are much stronger than what you are advising him to use, which is a simple rivet, which I can guarantee will not last nearly as long. I have used Rivnuts on commercial vessels(passenger carrying) for over 15 years. The lanocote is good but not for longevity, we have put it on fasteners and pulled them off a week later to find that it is has washed off, a great product that breaks the fasteners free from the Rivnut and makes a watertight seal on the threads and LASTS is Rectorseal 5 on the threads. Yes some poorly installed rivnuts can spin after awhile, but that is in terms of years, rivets just don't last as long, I can attest, but the rivenut shoulder just needs to be drilled off, without changing the hole size and you can reinsert another Rivnut. It's all about proper installation. I do think that a machine bolt and nut work best if you have that accessibility though. Thanks for the differing of opinions though, it makes for great conversation.

 

[centerline]

Again, Rivnuts are much stronger than what you are advising him to use, which is a simple rivet, which I can guarantee will not last nearly as long. I have used Rivnuts on commercial vessels(passenger carrying) for over 15 years. The lanocote is good but not for longevity, we have put it on fasteners and pulled them off a week later to find that it is has washed off, a great product that breaks the fasteners free from the Rivnut and makes a watertight seal on the threads and LASTS is Rectorseal 5 on the threads. Yes some poorly installed rivnuts can spin after awhile, but that is in terms of years, rivets just don't last as long, I can attest, but the rivenut shoulder just needs to be drilled off, without changing the hole size and you can reinsert another Rivnut. It's all about proper installation. I do think that a machine bolt and nut work best if you have that accessibility though. Thanks for the differing of opinions though, it makes for great conversation.

i will guarantee anyone who has had 15 years of experience (or even a few months) with rivet nuts or rivnut as the originals were called, has had many problems with them and knows they have no place on a small pleasure boat.... the automobile and truck industry has been using them for years, so its easy to ask any body shop who has had years of experience with them about their track record (or you can just ask me).... (properly installed ones are subject to the same failures where corrosion is a factor) and no one seems to like them and everyone knows their inherent flaws, but in some cases its the cheapest option of making the attachment.

I will concede that its not usually the strength or holding part that is the problem, but the high probability of failure in the corrosive environment and the degree of damage that will be caused when the fasteners need to be removed and the rivnut spins.... then repairs are needed and if you cant get the backside to hold the rivnut, it has to manually be ripped out and repaired correctly... and if you can hold the nut, the hole is always stripped to big for any repair other than (1) drilling the hole out and inserting the next size up for a larger fastener, or (2) welding the hole shut and making the repair correctly, or with another rivnut....
they have their uses but it should never be used where a failure of it is going to cause undue expense to repair it.... when something so simple can be used in its place... they're failure rate is too high especially where corrosion is could be an issue....
as for the washing out of the lanocote on threads of a properly seated fastener, above the waterline.... it will take a couple of years before it dries out enough to even become less effective..... but that doesn't mean its the absolute best thing to use, but every small boat sailor should have a container of it, or something very similar, for its many uses.... and know when and where to use it. its handy stuff.

and properly installed poprivits will last many, many years, (as will the rivnuts).... but the pop rivits can very easily removed and replaced when you have a doubt about their structural integrity. even when corroded, loose and jiggly, or snug and tight.....

i meant no disrespect to you when I replied as I did, but the rivnuts just aren't a good idea on open aired boats.... almost all of the commonly available fastners are steel and not aluminum, but in the application you stated as in bolting benches down inside, i can see the practical application of them.... and they should work well, until you need to remove the bolt and the threads are jammed.....

 

[DougM]

Pop Rivets are a logical choice, but need to be sized for both the metal thickness and strength requirements.The only caveat to that is the difficulty of removal if one must disassemble a riveted joint.

One example is the brilliant thinking on the part of the manufacturer who installed the steaming light on my mast with pop rivets. Unfortuately the bulb in that fixture must be changed from the back. That means going up there with a drill to drill out the rivets and remove the fixture, unscrew the back of the fixture to get at the bulb and replace. That only leaves the question of how to properly reattach it knowing that it will have to come off again some day.

 

[Chris Patterson]

In a situation like that, I would definitely put back in a stainless sheet metal screw. I always use anti-seize on these little buggers, but a mast light is never going to see much of a load. This is an item that DOES need to come off on occasion, so a rivet is impractical.

 

[thinwater]

One important, often fatal, flaw of sheet metal screws and to a much lesser extent machine screws is the sharp point on the inside of the spar. If there are either unrestrained wires or lines inside the spar you cannot use anything sharp.

On smaller boats 3/16-inch pop-rivets are very well proven, but the design must make sense. The load needs to be almost entirly in sheer and there must be enough of them to limit the load to about 200 pounds each. Corrosion should not be a factor--I've seen them on ancient beach cats that have spent decades on the beach--and removal every 10 years for equipment removal is a breeze--they drill out with a 3/16-inch bit in moments (if they spin, grab the head with vice grips, if the last bit won't drill, punch it through), unlike machine screws which tend to seize after a decade.

Tapping depends on wall thickness. While it can be the best answer on the thick-walled mast of a larger boat, suggesting it on the thin boom of a trailer-sailer is probably incorrect. Any galling or missthreading and the screw is worthless. A pop-rivet will be more reliable and simpler.

 

[jibes138]

For corrosion protection use Zinc Chromate Primer on screw threads that are steel on aluminum. This is standard practice on aerospace applications. Look up TT-P-645, costs about 95 bucks a gallon but I'm sure you can get it in smaller containers. It is a yellow color. Don't use anything else except zinc chromate primer, this stuff works. There may be other grades of the material but you most definitely want zinc chromate primer for any steel screw going into an aluminum hole.

 

[dscribner]

I installed a pad eye at the top of my mast and thru-bolted it. Here's what I did:

I got a small piece of aluminum channel, the inside dimension was almost snug on the flats of the nuts.

I drilled holes thru the channel, coated the bolts with Vaseline and bolted the pad eye on with SS screws and SS Nylok nuts. Then I potted the nuts inside the channel with epoxy.

After drilling the mast for the pad eye, I faced the holes down, measured from the base of the mast to the holes and marked this on a few lengths of PVC.

I taped the channel to the PVC and slip it into the mast, up to the mark. As soon as I started both screws, there was no problem of the channel spinning so I tightened them well and yanked out the PVC.

If you needed to, it would work on a 10' boom as well as a 30' mast.

 

[bffatcat]

Attaching a pad I to an aluminum mast or boom

I wouldnt use a bolt in this situation. The section on an aluminum mast or boom are too thin
Listen to Bill Roosa: Tap and machine screw are your best bet. That`s what I have always used successfully

 

[LloydB]

Use rivets when in shear, no excessive tension nor need to remove the part. Use bolts/machine screws when part is in tension and may need to be removed for inspection or replacement. Use screws to hold a part in place such that if it becomes loose you won't be....S...
BTW I am in favor of blind nuts BUT they must installed properly as where a pop rivet may give slight amount of fudge factor, installing a blind nut needs to be dead on. Thanks to Dremel a spinning blind nut can be fixed fairly easily altho maybe not so quickly.

 

[dscribner]

I wouldnt use a bolt in this situation. The section on an aluminum mast or boom are too thin
Listen to Bill Roosa: Tap and machine screw are your best bet. That`s what I have always used successfully

When the material is thin there is nothing to tap, nothing to grab. Thin material requires a thru bolt and washer to distribute the load or a rivet, preferably with a backing plate. The rule of thumb is 3 threads of engagement. A 1/4-20 machine screw (sometimes erroneously called a bolt) would require 3/20" (0.156) material to be considered fully engaged. Another option is a drive rivet. Instead of pulling the mandrel and snapping it off, the rivet is pushed in and the pin is driven in with a hammer. VERY good in sheer and pull-out.

 

[centerline]

I wouldnt use a bolt in this situation. The section on an aluminum mast or boom are too thin
Listen to Bill Roosa: Tap and machine screw are your best bet. That`s what I have always used successfully

if its too thin to use a bolt, nut and washers, it will never be a candidate for successful drilling and tapping...... or any other fastener.

 

[kenn]

Use aluminum pop-rivets for permanently attaching hardware to an aluminum boom or mast. Drill the right-sized holes, and add aluminum backing washers when you can.

I personally wouldn't put long-term trust on a SS machine screw tapped into aluminum. Unless maybe it's a fairly large screw going into 1/4" or more of aluminum.

Pop-rivets are easy to drill out, as long as they aren't spinning in the hole.