IMO, paint thinner is a general category of products such as mineral spirits, turpentine, naptha and others for thinning paint. In the case of the liquid sold as "paint thinner" you would have to check the label to see exactly what is inside the container but I'd bet most of it, if not all, is mineral spirits.
What is the difference between Mineral Spirits and Paint Thinner? What other names is it known by?
Answer: Mineral Spirits has fewer aromatic solvents while other similar Products-Paint Thinner, Varsol® - contain higher concentrations. Both are petroleum distillates, are generally interchangeable, and are available in different grades
Good question and I had the same recently when I decided to make my own wipe-on poly.
I visited HD and read the uses on paint thinner, mineral spirits, and Varsol. Paint thinner and mineral spirits were identical for uses and almost the same in price. Varsol was the only one showing a use for thinning polyurathane and of course it was more expensive. All were made by the same company.
I not really sure what the differences are but I know the all do the same job.
You can use paint thinner, mineral spirits and Varsol interchangeably for things like cleaning brushes. There is a difference between them, though. Varsol is a little "cleaner" than mineral spirits, which is a little cleaner than paint thinner. That's why Varsol is specifically okay for thinning oil-based polyurethanes and most paint thinners and mineral spirits don't list that as a use. You can actually use them for that, but if your results aren't what you hoped for don't blame the company.
I pay the little extra for Varsol (actually I pay even more and get the low-odour Varsol) because I get a little better results when I use it to thin poly.