Table 1 (IMAGE) Journal of Neurosurgery Publishing Group Caption Descriptions of each drill classification. Credit Credit: © 2017 AANS. Usage Restrictions Permission must be requested if you wish to reprint. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.