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I had to remove the plate (removing the screws) to do some unrelated repairs. Now I am concerned that the screws will not hold up as well, and I don't want that metal plate to fall on someone's head.

I researched the topic, and came up with dowels - 1/2" diameter - that will be hammered into the wooden board (into pre-drilled 1/2" holes). Then the 1/4" screws will go into the dowels.

Is there a way to validate that this will give the right strength?

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    A) it's hard to picture what you're describing, maybe edit in a picture. B) What do the screw holes look like and why type of wood are they in (there's a difference between hard woods, construction SPF, and MDF/particle board), and C) this really doesn't seem to be a woodworking topic and may be better suited for Home Improvement. D) Is there something else attached to the metal plate or is it just there?
    – FreeMan
    Commented May 2 at 18:01
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    Often, the solution for a torn up/stripped screw hole is to use a fatter screw (say 3/8" or 1/2") to give the screw some fresh wood to bite into.
    – FreeMan
    Commented May 2 at 18:02
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    Is the wood actually damaged from removing the screws? If not, I would be hesitant to do something that removed wood. By filling the holes with dowels you're going to be screwing into end grain, which has less holding power than cross grain. Also, no way simply hammering dowels into holes is going to be stronger; you would at least want to glue them in.
    – user15487
    Commented May 4 at 12:36

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Now I am concerned that the screws will not hold up as well

You should really only be concerned if you damaged the threads in the wood that the screws created in the first place.

Despite much hand-wringing about returning screws to their holes after removal, in reality screws going into hardwoods especially (but even softwoods) can often be inserted, removed and reinserted multiple times without any issues, as long as you're careful about it. The main thing is that you don't over-torque when tightening the screws, all too easy these days when most (?) no longer tighten screws by hand.

If there is slight damage to the threading in the wood — or even if you only suspect there is — it can be reinforced quite a lot using superglue or epoxy. Typically this would mean you just dribble some glue into the holes and let it set before the screws go back in, but as this appears to be an overhead application this may not be practical here.

Without this, use longer screws (quite a bit longer) if this is possible. You can also go up a gauge, but you have to be sure you don't select a screw that's merely a little larger than what was there originally. Of course the belt-and-braces thing is to use fatter and longer screws, if possible.

I researched the topic, and came up with dowels..... Is there a way to validate that this will give the right strength?

There is, if for example you could find the data for withdrawal resistance for the screws you're using. Then basically subtract 1/4. Despite widespread belief to the contrary, the withdrawal strength of screws going into end grain is quite uniformly 75% of the withdrawal strength of the same screw into long grain, all other factors being equal. See Endgrain screw withdrawal force for more on this.

The other way is of course to test it empirically yourself. Run a test on single screws, find the withdrawal force and multiply it by five. If you want to be more cautious then test a pair and see if the results for single screws do scale up.

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  • Or, to solve the end-grain pull-out issue, open the ceiling, drill holes through the joists horizontally, drive dowels into the holes, drive the screws through the long-grain of the dowel. :)
    – FreeMan
    Commented May 3 at 13:41
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    @FreeMan, well if one is going that far, nuts and bolts surely? ^_^
    – Graphus
    Commented May 4 at 5:58

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