Here are my dimensions for a 4-hole #whistle that plays G pentatonic scale (an “intuitive instrument,” as they say): G, A, B, D, E—and then, an octave higher, G, A, B (and even D, with the finger-holes covered, as the 3rd harmonic). Nice sound, easy to play, not that hard to make.
Bamboo (from a gardening store) with an inner diameter of 12 mm and a wall thickness of 3 mm.

#flute #DIY #bamboo #instrument