Abstract: A component of variable capacitive reactance of the non-rotating piston trimmer type a support bushing of which confines an adjustment screw to endless rotation but zero displacement, by which all damage to the mechanism is avoided by either breakage or wallowing. This screw possesses both threaded means to engage a piston which resists, but does not prevent, rotational and axial motion by engaging the inner wall of a tubular dielectric with a clutch and stopping means to limit both directions of travel of said piston within the dielectric, said stops of which, cojoined by force imparted by the clutch, translate the piston's travel from axial to rotational when they are engaged.