The most popular of handy mechanic fastener looseners is WD-40. It is a good idea to know what you are using and how to store it, precautions in its usage, and the handling of emergencies such as eye contact.
This is all I could find on the web for a MSDS:
WD-40's formula is a trade secret. The product is not patented to avoid completely disclosing its ingredients. WD-40's main ingredients, according to U.S. Material Safety Data Sheet information, are:
51% Stoddard solvent
25% liquefied petroleum gas (presumably as a propellant; carbon dioxide is now used instead to reduce WD-40's considerable flammability)
15+% mineral oil (light lubricating oil)
10-% inert ingredients
The German version of the mandatory EU safety sheet lists the following safety-relevant ingredients:
60–80% heavy naphtha (petroleum product), hydrogen treated
1–5% carbon dioxide
It further lists flammability and effects to the human skin when repeatedly exposed to WD-40 as risks when using WD-40. Nitrile rubber gloves and safety glasses should be used. Water is unsuitable for extinguishing burning WD-40.
Wired published an article giving the result of gas chromatography and mass spectroscopy: "What's Inside WD-40? Superlube's Secret Sauce
I'm going to list all the other products many of us tractor guys have in our shops. Save a copy and print out for handy reference in your barn, shed, garage, or shop.