Go look up the MSDS for it and it should list what solvent the base is. (I think it may be Xylene but it has been a while and I don't remember for certain.) The thinner will need to ideally incorporate whatever that solvent base of the paint is. If you do not have the MSDS or cannot find it online, try giving FMS a call....even though it is an older version of the product, Mike Sweet will likely still have that information around or at least know how you can find it.