Bolt shear strength

Hanging a 4 x 8 foot, 3/4" plywood tool board. What are the shear failure ratings for common 5/16 and 3/8" lag screws? IOW, how many
bolts per each 100 lbs load would be needed to provide a worry-free 2 or 3x safety margin?
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Dear Dr. Rev. Chuck, M.D. P.A.:

Worry about the plywood, not the bolts. Can you describe "hanging" a little more clearly? What is the orientation of the board, the support you are putting the bolts through, and the orientation of the "per 100 lbs load"?
Are we creating a gallows for Mr. Wittke (alias EinsteinHoax) or some more permanent structure?
David A. Smith
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snipped-for-privacy@aol.com (formerly) wrote:

On a wall, with bolts driven through to wherever I can locate a stud.

Horizontal.

2 x 4 divider wall resting on a concrete slab, the slab resting on planet Earth.

Evenly distributed over the whole panel. Or approximately so.

The gallows comes later. I'm still behind schedule a month on the electric chair.
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So you are hanging a board on a wall but the board is to be horizontal? So the wall is presumably horizontal too. That's a curious definition of the word "wall". Maybe "ceiling" or "floor" would be more appropriate?
Dave Baker - Puma Race Engines (www.pumaracing.co.uk) "How's life Norm?" "Not for the squeamish, Coach" (Cheers, 1982)
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"Dr. Rev. Chuck, M.D. P.A." wrote:

That's be a celing or floor.
The screws are loaded in tenion not shear then. So you need to the tensile strength of the screw, not the shear strength.
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On Tue, 5 Aug 2003 21:28:09 -0700, " snipped-for-privacy@aol.com \(formerly\)"

He's making a loft and he's fantasizing about sharing it with a hot babe. Let's see, 350 pounds max (unless he has a fat fetish) + force of thrustration (frustration relief with a 200 pound max load is more likely) ....
5/16 bolts with washers will work fine.
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Not sure how you arrive at that figure. If the bolt is the correct length, i.e. all the threaded portion is within the wall then the shear area would be the main body of the bolt with an area of 0.077in^2.
Dave Baker - Puma Race Engines (www.pumaracing.co.uk) "How's life Norm?" "Not for the squeamish, Coach" (Cheers, 1982)
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Jeff Finlayson wrote:

For a 5/16" lag, assume 1/4" diameter section for the threaded portion.
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On Wed, 06 Aug 2003 07:58:40 -0500, Jeff Finlayson

Please discontinue the sexual innuendo.
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bob wrote:

Lots of imagination for a troll.
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On Sun, 16 Nov 2003 22:15:32 -0600, Jeff Finlayson

Which of us has more patents?
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I think a screw is defined as being held by threading into a material, while a bolt is defined as being held by a nut (ref Shigley, among others) . I.e., look at it as a definition of application of a threaded headed device, rather than the name of the device itself, e.g., a 1/4-20 2" hex head can be used either as a bolt or a screw.
Flat head wood screws, for example, all have unthreaded shanks.
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Hobdbcgv wrote:

Yea probably not a general definition really.

I can't find anything in Shigley's ME Design book that agrees with that. It may be buried somewhere. The book uses the terms screw and bolt almost interchangeably.
A power/lead screw is fully threaded and is referred to as a screw not bolt. Aerospace fastener specs (NAS, MS, ..) refer to fasteners with unthreaded shanks as bolts and fully threaded fasteners as screws.

Probably an exception. They would not be referred to as bolts since they have pointed tips.
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Dear Jeff Finlayson:

while a

It
bolt.
This is what the trades use for a definition too.

device,
can be

In those cases, the unthreaded portion is to provide a bearing surface when joining two or more "boards".
Another exception is a carriage bolt, which is almost always threaded all the way up, and is always called a carriage bolt.
All rules have exceptions, probably even this one! ;>}
David A. Smith
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An unlikely but helpful resource for this type of information is a small book published by Bowman Fasteners called "Fastener Facts". I'm quite sure they deal at length about shear strength. How the fastener is used also needs to be considered. A properly torqued through bolt with nut behaves differently than a bolt threaded into a hole. Industrial Fastener Institute's "Fastener Standards" also has a section on shear applications.
The bolt vs screw debate is primarily a personal preference thing in my opinion. You can find a definitive source to support almost position. When in doubt, I'm frequently inclined to defer to Machinery's Handbook, but in this case I'd use IFI's "Fastener Standards" for questions on definitions as they have taken the lead in this area. I'll bet that Machinery's Handbook will agree with IFI as Machinery's Handbook is just a compilation of data from other sources.
Jon Juhlin

it.
material,
that.
almost
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all
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snipped-for-privacy@aol.com (formerly) wrote:

    The previous poster is correct. A screw is designed to be turned into something, whether it be a threaded hole, a piece of sheet metal or a piece of plywood. A bolt is designed *not to turn* but to have a nut (and generally a lubricated nut) turned onto it. There is a difference in the ultimate sheer and tensile strengths of equally sized screws and bolts. Bolts are generally less able to withstand torsional loads since they are primarily intended to withstand the tensile load applied by the (lubricated) nut. While it's not always easy to tell the difference, many bolts do not have the radius at the interface of the shank and head that most screws have.

    That's misleading because, while many bolts *do* have an unthreaded shank, the fact of an unthreaded shank does not make it a bolt. The reason for the unthreaded shank is because the bolt is intended to go into a clear hole and have the nut apply the holding load from the other side so there is no need for threads, where as a screw is intended to draw down against it's own head and if there were an unthreaded shank it couldn't be tightened up against the piece it is intended to hold (unless there were washers or some such).

    No, they are screws because they are intended to tighten up against their own heads. The unthreaded shank on a wood screw is intended to take the place of a lock washer, the tight interference fit preventing it from backing out.

    Not really...see above.

    Not correct, "carriage" bolts aren't threaded all the way up, they all have a square shank which prevents the bolt from turning as the nut is tightened...
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We may have a language problem....
English use of the word bolt donates a fastener with a shank. a set screw will not have a shank, and is frequently abbreviated to screw. These only apply to machine screws.... I.E. threaded fasteners with constant diameter.... a coach bolt may or may not have a shank, but will have a square head, and a tapering thread.
I think the terms are not really defined.... and if they are used in different ways by different people then they can *never* be relied on as a sole description, and if it is important the way it is being used the term must be defined as it is used.
-- Jonathan
Barnes's theorem; for every foolproof device there is a fool greater than the proof.
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"Jonathan Barnes" snipped-for-privacy@ATnetcomuk.co.uk

I. There's no reason you can't have a set screw with a "shank" (unthreaded portion of its length).
And

II. The carriage bolts I'm familiar with (New England) have a round head under which there is a short, squared length, with no point at the threaded end. (There's also a varient on theme called the "lag screw," which has not been mentioned yet in this thread.)
And

III. I agree. This discussion is about usage, which is never screwed down tight. "Bolt" and "screw" are generic terms; they have multiple meanings that won't be pinned down by MH or some trade text.
Frank Morrison
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There's no reason you can't have a set screw with a "shank" (unthreaded

In England, a set screw is always fully threaded .
-- Jonathan
Barnes's theorem; for every foolproof device there is a fool greater than the proof.
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Dear Jonathan Barnes:
wrote in message

A short search comes up with this UK site: http://www.rimmerbros.co.uk/herald/11a.htx ... look closely at item 4, identified as a "set screw". It has both a head and a shank.
Everyone's hands are dirty, apparently.
David A. Smith
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