A rotatable body (300, 400) comprising: a rotor; and n buckets for converting energy of flowing steam into mechanical work, each bucket configured to be coupled to the rotor in a tangential entry manner, wherein the rotor is configured to support each of the n buckets coupled to the rotor, wherein the rotor comprises: a rotor wheel having a circumferential surface on which a tangential entry is provided and comprising a rotor dovetail tenon extending in a circumferential direction of the rotor from one side of the tangential entry to the other side of the tangential entry, the rotor dovetail tenon having a gap at the tangential entry, and an adapter configured to couple an nth bucket (400(n)) of the n buckets to the rotor and comprising an axial dovetail tenon and an adapter dovetail tenon configured to fill the gap in the rotor dovetail tenon when the nth bucket (400(n)) is coupled to the rotor such that the rotor dovetail tenon and the adapter dovetail tenon form a unified annular dovetail protrusion protruding radially from a circumferential surface of the rotor, wherein the rotor wheel further includes an axial dovetail mortise extending in an axial direction of the rotor and formed under the tangential entry, and wherein the axial dovetail mortise is configured to receive the axial dovetail tenon of the adapter in an axial direction of the rotor. a rotor; and n buckets for converting energy of flowing steam into mechanical work, each bucket configured to be coupled to the rotor in a tangential entry manner, wherein the rotor is configured to support each of the n buckets coupled to the rotor, wherein the rotor comprises: a rotor wheel having a circumferential surface on which a tangential entry is provided and comprising a rotor dovetail tenon extending in a circumferential direction of the rotor from one side of the tangential entry to the other side of the tangential entry, the rotor dovetail tenon having a gap at the tangential entry, and an adapter configured to couple an nth bucket (400(n)) of the n buckets to the rotor and comprising an axial dovetail tenon and an adapter dovetail tenon configured to fill the gap in the rotor dovetail tenon when the nth bucket (400(n)) is coupled to the rotor such that the rotor dovetail tenon and the adapter dovetail tenon form a unified annular dovetail protrusion protruding radially from a circumferential surface of the rotor, a rotor wheel having a circumferential surface on which a tangential entry is provided and comprising a rotor dovetail tenon extending in a circumferential direction of the rotor from one side of the tangential entry to the other side of the tangential entry, the rotor dovetail tenon having a gap at the tangential entry, and an adapter configured to couple an nth bucket (400(n)) of the n buckets to the rotor and comprising an axial dovetail tenon and an adapter dovetail tenon configured to fill the gap in the rotor dovetail tenon when the nth bucket (400(n)) is coupled to the rotor such that the rotor dovetail tenon and the adapter dovetail tenon form a unified annular dovetail protrusion protruding radially from a circumferential surface of the rotor, wherein the rotor wheel further includes an axial dovetail mortise extending in an axial direction of the rotor and formed under the tangential entry, and wherein the axial dovetail mortise is configured to receive the axial dovetail tenon of the adapter in an axial direction of the rotor.