1. Long Life. 2. Various Sizes Available Our impregnated bits are manufactured to give optimum penetration rates ... the formation to be drilled. When order, please read .Size Available: "Q" series:A,B,N,H,P/ATK,BTK,B3 ... 9/16,NWD4,412F,SK6L146,TT46,TB56,TS116,CHD101All Chinese Sizes