You know... I even detailed the procedure of installing the lag screws, so there wouldn't be any confusion (knowing Ernie would be reading the post).
What does Ernie do: pull out lag screws that don't have threads to the cap.
I honestly don't know what those type of lag screws would be good for? But I have never in my life, used a lag screw that 'didn't' have the threads to the end.
Thanks for playing Ernie!

I dragged those out because that's what lag screws look like in general. A 3" lag can have almost an inch of unthreaded shaft, but what matters here is the actual bolts used.

I was not trying to make up a reason not to use lag screws. The screws themselves present the reason not to use them, at least not in anything as shallow as plywood.

You can find lag bolts with more thread than the example Ernie posted.

[Link: krfastenersupply.com]

Like I said, every lag screw I have ever used has had the threads to the end.
I have seen those type of lag screws in Lowes or Home Depot that do not have threads to the end. I have never bought them, nor understood what they would be used for and why someone would buy them.

It's an articulated mount now. I'm going to toggle.

Thanks for the input everyone.

Craig

Presumably you're joining something with some thickness to something much thicker.

Let's say you're joining two pieces of wood, each a 2x4, positioned so they look like a T. You'd take a 4" lag screw, go through the 1 1/2" thickness of the top of the T, then sink 2 1/2" into the other 2x4.

There is ZERO reason for threads for the entire 1 1/2" near the head. 4" bolts usually have about an inch with no threads.

Shorter lags are presumed to be used to mount thinner things, so there's less shaft without thread. Still, it's presumed that what you're mounting has SOME thickness to it.

...so I looked up what lag screws ARE DESIGNED FOR and found [Link: provenproductivity.com] in about ten seconds. I've added the italics.


I don't understand the mention of lag screws having nuts, but the rest of this description says that it is normal for lag screws to have a smooth portion of shaft near the head. Also, they're meant to hold much heavier loads than we use them for.

In other words, hardly any of us are using lag bolts correctly. Now it's time to look into other bolts and screws!  But Togglers are as good or better than lag bolts for most of our needs.

This is 1 of the lag screws, I generally order and have on my truck:
[Link: fastenal.com]:"600000 Fasteners"|~ ~|categoryl2:"600051 Screws"|~ ~|categoryl3:"600021 Lag Screws"|~ ~|sattr06:^"Hex Washer"$|~

This is a 2nd kind of lag screw I keep on the truck:
[Link: fastenal.com]:"600000 Fasteners"|~ ~|categoryl2:"600051 Screws"|~ ~|categoryl3:"600021 Lag Screws"|~ ~|sattr06:^"Hex Washer"$|~

I also have a handful of 3/8" x 6" and 3/8" x 8" lags just incase I run into a situation.
This along with dozens & dozens of other different kinds of screws, bolts, etc... I have several totes sorted & full. And a canvas bag for the larger specialty ones.

Who cares how much /width isn't supported? If it's attached to studs that are 16" O.C. at two or more points in the outer 1/3 of the panel (one at each end of the panel) it's not coming off unless the lags are too short to hold when some extraordinary force is applied. If the installer uses a small particle of their brain (AND the wall's construction somehow allows it), the mount will be able to use at least one stud.


The length of the screw that's between the mounting plate of a mount and the threaded toggle isn't in any material or fastener that will hold it, either- at least the lag only loses 1/4" and the toggler only has ~1/4" of thread engaged, in total.


Lag bolts work as well as anything, as long as they're sized correctly for the weight of the item being mounted and the materials they're threaded into. The amount of force needed to cause bolt failure is never going to be reached unless an insufficient number is used, they're too small and the weight being supported is excessive. Seems redundant, but if each condition is marginal, exceeding any of the others will cause failure. One difference between the Toggler and a lag bolt is in the thread- fine thread is less likely to back out by turning purely because of the pulling force at the top than coarse thread and if any kind of lubricant is used on lag bolts, this it possible, although still a rare occurrence. If the material fails where the lag bolt threads are holding, it doesn't have the benefit of more surface area, the way a Toggler or a nut and washer would (if it could be through-bolted).


In either case, a lag or Toggler isn't using only tensile strength to hold, it also uses friction at the threads and the bolt's shoulder, resisting rotation from the tension. The key to success is in choosing the correct size, so the threads don't shear the material they're engaged with and the weight of the item being mounted won't exceed the tensile strength of the bolts at the top (since the ones at the bottom are barely doing anything).

I see we're being bold this morning!

Well, he said

So your premise is wrong. Why do people write "if" and then state something that is not the case?

Who cares? Well, if the plywood is not supported and it can be pulled on enough to bend or bow, that bend will put extraordinary force on the bolts that are furthest apart. You'd then want those bolts to be extremely strong against pullout.


Even with largish brain particles in use, there is no framing behind this section of the buildout. Your conclusion is correct except it's based on an incorrect starting point, which is framing behind the plywood.


This leaves the lag being held by, say, 1/2" of wood while the toggler is being held by less than 1/4" of steel. The pullout resistance of the steel is MASSIVE compared to the pullout resistance of the wood. Remember the numbers I quoted?


This is completely correct. Remember that pullout figures for lag bolts are in the range of inches, though, and this is WAY under an inch of lagged thickness.
| The amount of force needed to cause bolt failure is never going to be reached unless an insufficient number is used, they're too small and the weight being supported is excessive.
Again, totally correct. You're ignoring the fact that wood will allow pullout WAY before steel toggler threads will allow pullout. I doubt either BOLT will fail, but a bolt mount is a system that depends on the bolt AND the substrate.
| Seems redundant, but if each condition is marginal, exceeding any of the others will cause failure. One difference between the Toggler and a lag bolt is in the thread- fine thread is less likely to back out by turning purely because of the pulling force at the top than coarse thread and if any kind of lubricant is used on lag bolts, this it possible, although still a rare occurrence. If the material fails where the lag bolt threads are holding, it doesn't have the benefit of more surface area, the way a Toggler or a nut and washer would (if it could be through-bolted).
Sounds like you're advertising Togglers here. So was I.

| In either case, a lag or Toggler isn't using only tensile strength to hold, it also uses friction at the threads and the bolt's shoulder, resisting rotation from the tension.
And the Toggler has MUCH greater resistance to pullout than a lag.
| The key to success is in choosing the correct size, so the threads don't shear the material they're engaged with
"Shear the material"? Shear is at right angles to the bolt, so that would be a mount moving downward along the wall. That is not an issue here, since the shear resistance of any of these bolts is HUGE compared to the load.


Right about the ones at the bottom. I sometimes see guys paying so much attention to the bottom bolts, not realizing that the bottom bolts really only resist shear forces. In fact, the lower plate of a mount actually pushes on the wall. Sometimes you see drywall having been crushed behind the lower parts of a wall mount. You need bolts along the bottom, but they have more to do with keeping the mount level than with keeping it off the floor!

Too much. Simple, Lags will work as will wood screws and togglers.
Just make sure plywood is mounted sufficiently with a high quality 1 1/4 drywall screw or smooth shank 16penny nail in each corner

Its 3/4" ply. just use 8 lags and walk away with a check forgetting you ever asked this question here.
Its not going anywhere and the back plate of the mount serves to prevent flex. I do this all the time with cabinets that have a moveable back wall.
10 years ago with those displays I might have thought twice but seriously, I wouldn't blink an eye today.

+1

This is going downhill fast.

There is no "in general"- fasteners are made very specifically, in many ways, to accommodate many uses. The ones you showed have fine thread at the shoulder- that tells me they're supposed to go into a hole that allows the thread to grab the steel or hold a washer.

Using 'if' is for hypotheticals and since it wasn't described in great detail, I wrote 'if'.


Who would install a piece of plywood for holding a TV without using some kind of framing behind it?


The Toggler can support more weight because the toggle covers a larger area (you know, F=M/A, but you do get tired of doing your guzintas and cypherin')- it's not the steel that resists more, it's the additional area of wood that's supporting the toggle.

| And the Toggler has MUCH greater resistance to pullout than a lag.

It's not the bolts shearing that's an issue, it's the material where the thread pulls outward- when a hole strips, it's because the thread has sheared it, or because the material didn't yield and the bolt thread sheared (very unlikely with lag bolts). Shear is when forces in opposite directions act on a material in a small area- it can be at the lower row of bolts, but they only see shear when all of the bolts are loose and the entire weight of the item being supported is hanging on them AND the lower row happens to be a bit higher than the upper but the only times I have seen a problem with that is when the face where the mount was placed wasn't backed up and nothing was there to support the pressure from tightening the bolts.

Extra bolts help and it's best for installers to avoid using the drill in the hammer setting when drywall is between the mount and the framing- seen it, didn't like the results. Some people seem to think that tightening bolts and oil filters are part of a contest.