Attention! - The tuning keys are conical, do not measure the key at the top square, measure at the point where the key meets the instrument (approximately the middle). The tuning keys and the appropriate tuning hammer are both conical on the inside, additionally the 4 walls inside at the middle are grooved, which causes confusion in dimensions. For example, 5.2 mm is measured at the extreme end, excluding the grooved interior. Of course, the opening at the bottom of the keys and hammers is wider than the middle part. Suitable for harp zither. White beech handle, T-Form. Suitable for keys with a diameter of 6.25 mm.