Significance: If flutes do not extend deeply into the small end of the log and the ingrown bark does not extend into the right cylinder, they are disregarded as grading defects.

In veneer logs, flutes are grading defects where the ingrown bark, extends into the right cylinder. Flutes have a tendency to spiral along the tree stem in elm and soft maple. If this spiraling exceeds one-half inch per foot (1.3 cm per 30.5 cm) of log length, the log is disqualified for veneer use. Where the ingrown bark extends into the right cylinder only for short distances, each such occurrence is a log grade defect, and a scaling deduction is taken.

In factory logs, flutes usually are treated in the same manner as veneer logs. Logs that have been dropped from the veneer class because of spiral grain should qualify for factory lumber logs. Where encased bark extends into the right cylinder, each occurrence is treated as both a grading and scaling defect.

In construction logs, if the encased bark enters the included timber in more than short disconnected streaks of the spiraling results in a slope of grain less than 1 in 12, the log is disqualified for the construction class.

In standing trees, careful examination is made for the two major features associated with flutes. First, the inclusion of ingrown bark is estimated; next, the severity of spiral growth of the flutes, appraised. These two features dictate the assignment of log classes where multiproduct logging is practiced.