[Gairloch]

It's my preferred brand of penetrating oil.

Originally Posted by wikipedia.org

Penetrating oil or penetrating fluid is very low viscosity oil. It can be used to free rusted mechanical parts (such as nuts and bolts) so that they can be removed, because it can penetrate into the narrow space between the threads of two parts. It can also be used as general purpose lubricant, or to clean or prevent corrosion. Use as a general-purpose lubricant is not advisable because penetrating oil is relatively volatile - much of the penetrating oil will evaporate in a short amount of time, leaving little residual lubricant.

Other uses include removing chewing gum, on metal stringed musical instruments, moisture displacement on electrical ignition systems, many gardening purposes, D.I.Y use.

WD-40, Liquid Wrench, Unilease, GT85, Kroil and CRC 5-56 are well-known brands of penetrating oil.