50/50. If you want to try it, a quart of each will do, to start. Acetone can be found in the paint section, ATF, cheaper the better. I watch for partial bottles, or, odds and ends of bottles at auctions, that a case will usually go for a buck. If you find you like as well as I do, you can buy the Acetone in gallons. Here, it's about $13 a gallon. I happened to catch a 2 gallon jug of ATF on sale at Rural King, for $18.
Just be sure you put it in a dispenser you can seal. I use a small dish detergent bottle, with a snap lid. Otherwise, the Acetone will evaporate. It will separate when it sets for a while, just give it a quick shake, and you're good to go.
I've used many types over the years, including PB Blaster, and Kroil, but this mix beats them both..!! Just don't get it on a painted surface, you don't want messed up. The Acetone will take paint off.