MK Diamond 168465 12-Inch Core Bit Extension, 6-1/4-Inch Made from high quality, heat treated steel for long tool life Allows for achieving greater drilling depths with MK standard or professional core bits More than one 12-Inch extension can be used to increase drilling depth Easy three step assembly 6-1/4 inch diameter Allows for achieving greater drilling depths with MK standard or professional core bits More than one 12-Inch extension can be used to increase drilling depth Easy three step assembly Made from high quality heat treated steel for long tool life