On Tue, 8 Jun 2010 07:51:30 -0500, "Joe J" wrote:

I'm attaching 2 x 4s to the studs in a finished garage. Finished with 1/2"
drywall. Are 3" screws long enough, I have a bunch leftover from a
different project? The 2 x 4s will be holding 5/8 plywood for shelves. Or,
should I just bite the bullet and go with 3 1/2?

Thanks

When choosing length, try to have about 1/3 of the screw in the piece
being fastened and the remaining 2/3 of the screw threaded into the
piece being fastened to. As the thickness of the lumber increases
though, this ratio can be reduced to 1/2 if absolutely necessary.

That's why only 2/3 of the shank is typically threaded on our 1" and
longer wood screws.

In your example the preferred screw length would be ~4-1/2" to 5"

Gordon Shumway

A Liberal is a person who will give away everything he doesn't own.