Penetrating Oil

It needs time to soak in. Repeated applications help. Heat can assist on stubborn bolts. Leaving it overnight on very rusty exhaust or suspension bolts often works better than force. Alternating between tightening slightly and loosening helps break the rust bond. If bolts still will not move, heat or cutting may be needed, which is a job for experienced hands.

Low viscosity lets it travel into tiny gaps.

It is flammable; keep away from heat. Clean off before applying thread locker.