To provide a tooth and an adapter, and a structural body and a method for mounting the tooth and the adapter capable of increasing a life against wear, eliminating the possibility of damage, and reducing a cost.

A projected mounting part 21 fitted into an adapter 10 is provided at the base part of a tooth in excavating direction, and a recessed tooth mounting part 11 fitted onto the tooth 20 is provided at the tip part of the adapter in the excavating direction. The recessed tooth mounting part 11 comprises a generally cylindrical recessed abut-on surface 12 having the axis thereof in the direction orthogonal to the excavating direction, and a projected part 14 is provided at the end part of the opposed surface of an opening part 13. The projected mounting part 21 of the tooth 20 comprises a generally cylindrical projected abut-on surface 22 having the axis thereof in the direction orthogonal to the excavating direction. At the time of mounting, the mounting part 21 of the tooth 20 is fitted into the tooth mounting part 11 of the adapter 10 from the direction orthogonal to the excavating direction.