A housing pivotably supporting an operating lever is mounted on a handle bar by a band. A nut with opposite end ears engaged in apertures formed in the ends of the band is held drawn into the housing by a bolt provided within the housing and extending through the nut in screw-thread engagement therewith to fasten the band to the handle bar. Each of the ears includes a shank projecting from each end of the nut and a flange formed at the outer end of the shank and having a portion remote from the center of the shank and a portion close to the shank center diametrically of the shank. Each of the apertures in the band is so shaped as to permit the flange to removably pass therethrough and to render the shank displaceable within the aperture, thereby making the band engageable with the inside surface of the flange.