Most people just hand-tighten their coax cables, let alone actually use a torque wrench to get the perfect torque. If you want to “do it right,” Wiha now makes a series of Cable Keys for use with our standard Torque Screwdrivers, designed specifically to prevent over-tightening of all sizes of HEX cable connectors.
Over-torque can possibly crush the insulation, as well as the center contacts and ground mating surfaces. Any change to those can alter the impedance and increase the VSWR. Under-torque can be just as bad if an air-gap is left in the insulator, or the center pin or ground mating surface isn’t fully engaged. This becomes a more significant problem with higher Gigahertz.