I would think for the tapped hole with machine type screw in wood the thread would need to be relatively coarse. Screws for aluminum often use a coarser thread than those for use in steel. The coarser thread give a greater thickness to the thread, thus a higher shear strength. Necessary lengths of engagements for screws is based upon the strength of the crew body vs the shear strength of the threads. It is usually desirable to have this proportioned so that if one Over Tightens the screw the screw itself will be popped rather than the threads stripped. The neded length ratio is going to be longer for wood than even for aluminum. Wood screws should of course not be taken ou & back in any more often than is an absolute necessity. Even in aluminum when it is desirable for the screw to be often taken in or out steel thread inserts are quite often resorted to.
