Wood shrinks and swells across the grain (width) of the board due to changes in moisture and temperature. This becomes a problem where boards are attached "cross grained", such as a table top mounted at the ends to a board running crossways (grain perpendicular). Hope this helps.

M60v3, VP100v3, QS8v3, EP350v4, Onkyo TX-NR905

M22v2, Vector Research VRX-9000 stereo

AxiomAir