Screw widths and weight limits

Submitted by solomonson on Fri, 11/12/2010 - 16:22

Ok, another one.  I'm now trying to hang the entry way shelf into studs.  I have hooks that can take up to 35 lbs.  I have 2 inch wood screws, number 8 width.  Does anyone know if there is a weight limit to the screws?  In other words, I want to be assured that I won't overload the screws (I am installing at least of them into a stud) and have the shelf come crashing down if I hang my diaper bag from a hook.  TIA once again.

Tsu Dho Nimh

Sat, 11/13/2010 - 04:59

The "shear strength", which is the amount of sideways force the screw can resist before it snaps, is high enough. The metal of the hook will snap before the screw does, if it's installed correctly.

The force on the screw is straight down, and snapping the neck of a screw is not easy.  (except for drywall screws, which are brittle) 

 

Most hanger failures are because the screw didn't get a good grip or because the load gets yanked from several directions and it slowly enlarges the screw hole and then the whole thing falls out.

 

1 - It has to have over half its length in the stud ... allowing 3/4 inches for the hanger and drywall, 2 inches is fine for general purpose hooks and light duty shelves. (I have seen shelves where the tenant was over the stud, but with a screw that barely entered the wood. It fell off the wall within a couple of days.)

2 - Drill a proper size pilot hole - I posted a table of screw size versus drilll size on here somewhere - so the stud doesn't split. Shoving a screw into a crack in the stud isn't very secure.

3 - Drill STRAIGHT into the stud. If you are at an angle, you may go through the corner of the stud. it's not a strong connetcion because the threads aren't all in the wood.

3 - Don't over-tighten it - if you start spinning the screws in the stud, it's a peg, not a screw and can wiggle out.

solomonson

Sat, 11/13/2010 - 07:17

Thank you so much.  How do you define "light duty" shelf?  We plan on hanging 2 heavy coats through the winter, a diaper bag, etc.  It's mostly pine with a beadboard back.  I would estimate the shelf itself weighs maybe 15-20 lbs.

Tsu Dho Nimh

Sat, 11/13/2010 - 10:37

Light duty ... something I'm not going to chin myself on :)  Ordinary wood screws have a shear strength of several hundred pounds, so they will be the last thing that comes off the wall. The boards would break before they did.

 

This one: http://ana-white.com/2009/11/p.....314.html  ???

 

You need screws long enough to go through the backing boards and the drywall AND still have more than half of it in the stud ... 2 1/2 inch would be better.

If  you mount it with 4 screws - 2 on each side, one near the top of the compartments and one near the bottom of the unit, it's not going to go anywhere. The screws share the weight and the screws prevent 'wiggle" if someone yanks a coat off the hook so it doesn't work its way loose.

The only problem would be if your beadboard is that thin cheesy stuff  and not real wood or shelf-thickness MDF ... that thin beadboard can't hold the weight of the shelf and it slowly rips  off the screws. They stay in the wall and the shelf hits the floor.

The way to deal with thin backing board is to install a couple of 1x2's, screwed in with pocket screws, at the top of the cubbies and the bottom of the cubbies. Screw through these. (look inside your kitchen cabinets - that's how they are probably mounted. Or screw them to the back of the shelf unit along the top and the bottom of the compartments and add a bit of trim to hide the extra depth.

solomonson

Sat, 11/13/2010 - 13:15

That's the one.  I'm not sure if the beadboard is the "thin cheesy stuff".  It's wood for sure and not fake.  Though the 1 x 2 plan you mentioned sounds easy enough.  I don't have a kreg jig for pocket screws, would regular screws suffice?  Thanks again for your help.  And I found your chart and have bookmarked it, thanks for making that!  It was super helpful.

Guest (not verified)

Tue, 03/27/2012 - 21:20

Can any one let me know where to search for screw take up weight spec/table ???

Guest (not verified)

Tue, 03/27/2012 - 21:22

Can Some one tell me where can I search for the screw take up weight spec/table??? Thank you.

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