counterbore- a bit for enlarging the upper part of a hole countersink bit,countersink bit- the cutting part of a drill; usually pointed and threaded and is replaceable in a brace or bitstock or drill press; "he looked around for the right size bit" ...
4.Effect of Bolt Hole Depth on Camshaft Bore of YZ4DE Diesel EngineYZ4DE柴油机气缸盖螺栓沉孔深度对凸轮轴孔的影响 5.Fasteners--Counterbores for hexagon bolts and nutsGB/T152.4-1988紧固件六角头螺栓和六角螺母用沉孔 6.Study on Sedimentary System of Kong Member 2 in Kongnan Area in Huanghua...