The TCI Tricone bits drilling for medium to hard rock formation. The medium formation TCI tricone bits features aggressive chisel tungsten carbide inserts on the heel rows and inner rows. This design provides a fast drilling rate and added cutting structure durability in medium to medium hard formations. The HSN rubber O-ring provides adequate sealing for bearing durability. The hard formation TCI tricone bits can be used to drill hard and abrasive formation. Wear resistance tungsten carbide inserts are used in the outer rows to prevent loss of bit gauge. Maximum numbers of hemispherical shaped inserts are used in all rows to provide cutter durability and long life.