... by CNC, and multi-heat treat, with premium alloy steel BQ,NQ, HQ, PQ core barrel,overshot,diamond core bit, China Drilling ... assemblies, synthetic diamond core bits, natural diamond surface-set core bit, PDC bits (core or noncoring), casing shoes, reaming shells, overshot ... , BTW, NTW, HTW, T2, T6 etc. Diamond core bit, reaming shell & shoe bit (syntheyic and surface-set, PDC) 4.Drill tool: hoisting ...