... wear resistance.2. High-precision metal seal.3. Locking roller ball, to adapt to high-speed.4. The use ... to the soft, medium and hard of various strata.7. Reasonable price and long working life.Size and types ... availableCommon sizes: 6, 6 1/2, 7 7/8, 9 7/8, 10 5/8, 12 1/4Various sizes ... precise delivery time) E. Bearing( Metal / Rubber) 9 7/8" Kingdream HAS 447G TCI Tricone drill bit with best ...