A: Ring test (sound test) is performed on the abrasive wheel to check for any hidden cracks. (Ref - COSWP - 18.19.3) Use of a cracked wheel can cause the wheel to break apart and send small pieces flying.To perform the test, balance the wheel on a shaft or screwdriver passed through the central hole, and gently tap the wheel with a light non-metallic implement near the edge, at four points around the circumference. A dull thud indicates a cracked wheel (unfit for use); a clear metallic ring indicates the wheel is sound.