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I have a projector screen which weighs about 8 kg (~17.6 lbs) and to light it up a little for when I don't use it I decided to mount a LED strip behind it. I already bought matching strips of wood (24 mm / ~0.9 inches). The screw head has to leave a space of about 2 mm (~1/10 inch) so that I can hook the projector screen.

The wall is no drywall, I suppose it is out of concrete or bricks. I've only put nails in it and I think I won't get them out if I have to...

The projector screen frame has two mounting holes in both top corners.

Which length and diameter should the screws have? Maximum diameter of the mounting holes is 11 mm (~0.4 inches)

wall diagram

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The screws needed depend on the lever forces they have to support. Can you describe the way how you plan to hang the frame (sketch, picture of)? –  Peter Ivan Feb 18 '13 at 19:04

2 Answers 2

up vote 1 down vote accepted

There is quite an 'overhang' of the screw (24 mm) from the wall. That's why you need at least 6 mm screws in diameter. It's head is about the maximum you have.

That implies 12 mm anchors, which are 60 mm long here.
The resulting screw would be 6x80, or 6x90, if you have longer anchors.

Remarks:

  • the overhang should be as short as possible, that's why you shouldn't push the anchor unnecessarily deep into the wall. Too big lever would strain the screw, the anchor and the wall.
  • I'd drill the hole not horizontally, but several degrees (5° - 10° from horizontal line) from top to bottom. It wouldn't let the screw to be pulled out when it settles (lowers its head) a bit.
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Thanks for both of your tips. Which angle do you propose? 80-70° or more close to 45° if 90° is horizontal. If the angle is lower I would need a bigger overhang. –  meilon Feb 19 '13 at 12:35
    
@meilon: I updated my answer. –  Peter Ivan Feb 19 '13 at 13:01
1  
I used 6x80 screws and it hold very well. Thanks for your help! –  meilon Feb 22 '13 at 17:49
    
You're welcome. If you find any answer or question useful, you can upvote it too. The community shows its opinion this way. –  Peter Ivan Feb 23 '13 at 20:18
    
But I can only do this if I have a reputation of at least 15... –  meilon Feb 24 '13 at 13:23

The screw should penetrate at least 1", more if possible into the material (concrete, brick, etc.). So if you have 24mm thick wood, and you want the screw to hit a depth of say 1.25" inch, you need ~24mm+32mm (1.25") +2mm (exposed screw) = 64mm (2 1/2") screws.

Now you need a plug or anchor that can accept this length of screw. As for size of screw, I'd use a #6 or #8 screw.

Another (easier IMO) option is to use a concrete screw that does not require an anchor - they are sometimes known as Tapcon's (common North American brand).

Make sure to drill the hole at least 1/4 deeper then needed.

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Why do I need to drill deeper than needed? –  meilon Feb 19 '13 at 12:36
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if its exactly the right depth, the tip of the screw will be up against concrete. also, all some the dust from drilling will remain –  Steven Feb 19 '13 at 13:10
    
Thanks for your help, too but I felt more comfortable with Peter Ivan's solution. I would give you a vote up if I could! –  meilon Feb 22 '13 at 17:50

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