Is it a hex head bolt? Are you using the long end of the hex wrench? Sometimes you need to use a piece of tube over the short end of a hex key in order to get enough torque to break a bolt loose. Ditto for as nut - sometimes you need to use a longer transverse lever such as a small socket wrench rather than a nut driver that lookd s lot like a screwdriver to break a nut loose. What tool are you trying to get this bolt or nut loosened with?

Cheers from Miele Man