Abstract: A unitary three-vane support bead (30) detunes the lowest-frequency transverse cavity modes, forcing resonances toward higher frequencies. Its impedance, compared with that of prior solid beads, is closer to the impedance of an air line. The bead is injection-molded in place, with a radial boss (35) at the radially outer end of each vane (32). Three apertures (14) in the outer conductor (11) capture the bosses, for economical but secure mounting; in fabrication these three apertures serve as injection gates. On its end (29) facing a mating device (65, 65f), the central conductor (21) has an axial bore (26) that holds a cylindrical sheet-metal spring (50). The outward-facing edge (56) of this spring protrudes slightly from the bore and is trimmed to form three distinct contact areas (52), each of relatively small circumferential extent, for kinematically stable engagement with the mating-device central pin (65).