Hollow shaft motor comprising: - a main body defining a central axis and including an outer face transverse to said central axis centrally defining an opening, - a shaft extending along said central axis internally to said main body, rotating about said central axis with respect to said main body and comprising a first coupling portion configured to be connected to an external shaft of a pump and a second coupling portion configured to be connected to said main body, - a bushing capable of being coupled to said first coupling portion, defining an prevailing expansion axis and including at least one housing extending along said prevailing expansion axis and suitable for housing said external shaft in such a way as to transmit, in use, the motion of said shaft to said external shaft, - first constraint means configured to reciprocally constrain at least rotationally about said central axis said shaft and said bushing and comprising a tooth protruding along said central axis and a groove extending at least partially along said central axis and configured to receive said tooth, said tooth being constrained to, or part of, one between said shaft and said bushing, and said groove being disposed on the other between said shaft and said bushing, - said first coupling portion including: - a cavity facing and accessible from said opening, developed mainly along said central axis and configured to host said bushing, - at least a first wall delimiting at least part of said cavity around said axis and configured to prevent reciprocal translation of said bushing with respect to said shaft transversely to said central axis, and said motor being characterized in that - said bushing comprises a base wall transverse to said prevailing expansion axis and comprising said tooth and said shaft defines a bottom wall transverse to said central axis, delimiting said cavity with said first wall and comprising said groove, said groove being at least partially counter-shaped to said tooth. - a main body defining a central axis and including an outer face transverse to said central axis centrally defining an opening, - a shaft extending along said central axis internally to said main body, rotating about said central axis with respect to said main body and comprising a first coupling portion configured to be connected to an external shaft of a pump and a second coupling portion configured to be connected to said main body, - a bushing capable of being coupled to said first coupling portion, defining an prevailing expansion axis and including at least one housing extending along said prevailing expansion axis and suitable for housing said external shaft in such a way as to transmit, in use, the motion of said shaft to said external shaft, - first constraint means configured to reciprocally constrain at least rotationally about said central axis said shaft and said bushing and comprising a tooth protruding along said central axis and a groove extending at least partially along said central axis and configured to receive said tooth, said tooth being constrained to, or part of, one between said shaft and said bushing, and said groove being disposed on the other between said shaft and said bushing, - said first coupling portion including: - a cavity facing and accessible from said opening, developed mainly along said central axis and configured to host said bushing, - at least a first wall delimiting at least part of said cavity around said axis and configured to prevent reciprocal translation of said bushing with respect to said shaft transversely to said central axis, - a cavity facing and accessible from said opening, developed mainly along said central axis and configured to host said bushing, - at least a first wall delimiting at least part of said cavity around said axis and configured to prevent reciprocal translation of said bushing with respect to said shaft transversely to said central axis, - said bushing comprises a base wall transverse to said prevailing expansion axis and comprising said tooth and said shaft defines a bottom wall transverse to said central axis, delimiting said cavity with said first wall and comprising said groove, said groove being at least partially counter-shaped to said tooth.