Abstract: The extension of the handle-bar stem is provided with a transverse aperture forming a collar for receiving and supporting the handle-bar. A clamping lug which extends from the collar toward the vertical arm of the stem has an upper face which defines with a lower face of the extension a slot splitting the collar. The lug and the extension are provided with apertures for the passage of a clamping device.The extension also has an axial cavity which is extended by an opening formed in the collar. The clamping device has one end hidden in the cavity and an opposite end hidden within the thickness of the clamping lug.