The key to any penetrating oil is surface tension. The lower the surface tension of the oil the smaller sized pore the oil will saturate and wet. Wetting is the operative function. Wetting reduces friction that prevents turning; much like dry clay soil wetting results in slick mud.
A test to show effececy is to take a rusty nail, 8/10 penny or so, and stand it head down in a jar lid and lean it against a cardboard box. Fill the lid with the product and watch to see if the liquid wicks up the nail. If it doesn't then it won't penetrate well. The one that wicks the highest is the best product.
I make an industrially available penetrating oil and it beats Kroiloil cold.
