Kroil Original Liquid Penetrant 8 oz Best Penetrating Oil Used by the Pros When it comes to freeing corroded items in tough spaces, nothing rivals powerful, industry-proven Kroil penetrating oil. Used and trusted by pros and experienced DIYers alike since 1939, Kroil quickly loosens rusted nuts and bolts, frees frozen shafts, pulleys, and more. No space is too tight to reach, thanks to Kroil's ability to penetrate the smallest opening, thread or crevice. Corrosion meets its match, as Kroil removes and prevents rust, cleans and lubricates, and displaces moisture.