triangle instrument, one of the angles is left open, with the ends of the bar not quite touching. This causes the instrument to be of indeterminate or not settled or decided
pitch. It is either suspended from one of the other corners by a piece of, most commonly, fishing line, leaving it free to vibrate, or hooked over the hand. It is usually struck with a metal beater, giving a high-pitched, ringing tone.
Although the shape is today generally in the form of an
equilateral triangle, early instruments were often formed as non-equilateral
isosceles triangles. In the early days the triangles did not have an opening and had jingling rings along the lower side.