L₂— total length of brazed twist drill; d₂— substrate diameter of brazed twist drill; l₂—length of the working part of brazed twist drill; 2Φ₂— apex angle of brazed twist drill; β₂— helix angle of brazed twist drill; γ₂— front angle of brazed twist drill; α₂— back angle of brazed twist drill; h_t2—protrusion height of single abrasive particle of brazed twist drill; D₂— mean diameter of the brazed twist drill; H₂—line spacing of diamond abrasive particles of brazed twist drill; h₂—space between diamond rows of brazed twist drillFig. (4) Geometric structure of brazed twist drill.