plate. The spacer plate is often constructed of metal, but spacer plates have been constructed of wood, bark, and ceramic. When positioning and securing the removable block with the strap, the use of a spacer plate provides and additional degree of control over the sound and tuning of the flute. However, it also adds a degree of complexity when performing the task of securing both the block and the spacer plate. Plains style vs. Woodlands style Various sources describe attributes of Native American flute that are termed "Plains style" and "Woodlands style". However, there is no general consensus among the various sources about what these terms mean. According to various sources the distinction is based on: whether the flute uses a spacer plate to create the flue of the instrument, whether the flue is in the body of the flute or the bottom of the block, the sharpness of the angle of the splitting edge, whether the finger holes are burned or bored into the body of the flute, the design of the mouthpiece (blunt and placed against the lips vs. designed to go between the lips), the timbre of the sound of the flute, or details of the fingering for the primary scale. Branch flutes While many contemporary Native American flutes are crafted from milled lumber, some flutes are crafted from a branch of a tree. The construction techniques vary widely, but some makers of branch flutes will attempt to split the branch down a centerline, hollow out the inside, and then mate the halves back together for the completed flute. Double and multiple flutes A double Native American flute is a type of double flute. It has two sound chambers that can be played simultaneously. The two chambers could have the same length or be different lengths. The secondary sound chamber can hold a fixed pitch, in which case the term "drone flute" is sometimes used. The fixed pitch could match the fingering of the main sound chamber with all the finger holes covered, or it could match some other pitch on the main sound chamber. Alternately, various configurations of finger holes on the two sound chambers can be used, in which case terms such as "harmony flute" or "harmonic flute" are sometimes used. Extending the concept, Native American flutes with three or more chambers have been crafted. The general term "multiple flute" is sometimes used for these