| 摘要 |
A bit for a rotary drill, the bit including a cylindrical body having at least two flutes provided therein, the cylindrical body terminating in a cutting end; and a cylindrical land defined by a peripheral face of the cylindrical body between adjacent flutes, the cylindrical land including a margin that is radially elevated relative to a remainder of the cylindrical land; the margin having a width that varies along the length of the cylindrical land. |
