The Stone Tools 4 way chuck key is the ideal tool for unlocking and locking of various, popular drill chucks to keep drill bits in place Each key is made of heat-treated steel with a stainless steel finish for an optimal combination of durability and hardness. Stainless steel adds rust resistance. Center square feature is ideal for opening acetylene tanks Includes 4 pilot hole sizes: 3/8" with 12 teeth; 1/4" with 10 teeth; 5/16" with 11 teeth; 1/4" with 11 teeth