Longitudinal material direction

The material direction that is parallel to the direction of grain orientation (grain elongation). For bar material, this direction is usually parallel to the longest dimension of the original uncut bar (i.e., as the bar originally came from the manufacturer). When the term "longitudinal" is used in this sense, it does not imply a specific relation to the direction of resonator vibration.

Horns are reported to have better fatigue properties when they are machined so that the stud axis is parallel to the longitudinal material direction.

Also see —
Long transverse material direction
Short transverse material direction