CRL Thundertwist™ "A" Taper Impak™ Drills are best for electric and pneumatic hammer drills. The high-quality standards set for their manufacturing and testing assures you of long drilling life and top performance. They achieve superior drilling results when used on limestone, brick, marble, concrete, granite, tile, slate or cinder blocks. Optional "A" Taper Adapter allows you to use these Bits in hammer drills requiring SDS-Plus. The #1 Drift Key is a special tool required to remove the chuck from a drill press.