... used in oil exploration, subterranean heat. Hydrology welling drilling and so on.3.It is almost suitable for hard ... rocks, such as limestone, dolomite, chert, firm sandstone, and firm anhydrite and so on.4.According to your request, all sorts ... in stock to meet your special need. 3.Sizes and types of drill bits we can privide: 60mm,65mm ... 8(10 5/8”),295.3(11 5/8”)311.1(12 1/4”),346.0 (13 5/8”),349.2(13 ...