A seat comprising a seat part and a height adjustment mechanism comprising a link having a bore which comprises at least one substantially radial notch, a revolving tube having a fitting portion placed in the bore, said tube externally comprising two axial stops in contact with the link on either sides, at least one of said axial stops consisting of a bead having a stop surface in contact with the link, and a support surface opposite from the stop surface, the fitting portion externally comprising at least one bulge extending into the notch, wherein the bead comprises at least one axial indentation in the support surface, facing the notch, said indentation being adjacent to the bulge.