The iron collar locked around the neck and the fingers were inserted between iron bars, as if the victim were playing the instrument. Depending on the seriousness of the offense (or the mood of the torturer), the bars could be adjusted from uncomfortable to excruciating. Public ridicule also played a part of the torture.
This device was always fashioned in the likeness of a musical instrument as the offense of the victim was invariably an auditory offense - disturbing the peace, swearing, partying, etc.
Trivia & Comment
Trumpets, fiddles, and flutes were the prevailing style, as these could be locked around the hands or neck.