Just an exerpt of an article posted on another forum. Thought it would be good info for wrenchers... "The April/May 2007 edition of Machinist's Workshop did a test of penetrating oils where they measured the force required to loosen rusty test devices. Buy the issue if you want to see how they did the test. The results reported were interesting. The lower the number of pounds the better. Mighty interesting results for simple acetone and tranny fluid! Penetrating oil . Average load .. Price per fluid ounce None ................. 516 pounds . WD-40 .............. 238 pounds .. $0.25 PB Blaster ......... 214 pounds .. $0.35 Liquid Wrench ... 127 pounds .. $0.21 Kano Kroil ........ 106 pounds .. $0.75 ATF-Acetone mix.. 53 pounds .. $0.10 The ATF-Acetone mix was a 50/50 mix (1 to 1 ratio)." The author of the original article has confirmed this on the MW forum. (General - The Home Shop Machinist & Machinist's Workshop BBS) Personally, I've used the ATF-Acetone mix and had very good results. I believe that what's happening is that the acetone breaks down the surface tension of the ATF which allows it to penetrate into the threads. Then the acetone evaporates, leaving the ATF to break down the rust a bit and act as a lubricant."