I'm looking at manufacturing a product that has a patent # clearly printed on the product. But after a little digging on google patents, it clearly says "Legal status Expired - Lifetime" with a "Grant date 1995-03-21". Am I in the clear to manufacture this product? What things should I consider before I produce thousands of units?
Am I in the clear to manufacture this product?
Not necessarily. Even if the marked patent is expired, there may be other patents (or designs) that are pending and in force, which would cover the product. The key way to assess this is to perform a freedom-to-operate search.
However, if you are intending to produce something which is identical to a product that has been available for more than 20 years, this risk is somewhat lower.
I suppose you intentionally did not mention the patent number, so you should expect only vague answers.
In most parts of the world, patents last 20 years from their filling date. This is the case, for example, for a European Patent (EP) or a Canadian Patent (CA).
Some other countries, like Brazil, have a provision that says 20 years from filling date OR at least 10 years from grant date".
In the US, before 1995 something similar was in force: "either 17 years from the issue date or 20 years from the filing date, whichever is longer" (Wikipedia, Term of patent in the United States). However, the filling date is not always so simple to establish. Was any priority claimed? Any provisionals filed? Is it a national entry of a PCT application?
Those are some general remarks about patent terms.
Beyond that, are you planning to manufacture within the territory that the patent is valid or outside of it? If it's a US patent and you manufacture in Germany, you are clear (provided that there is no similar patent is Germany either). Likewise you are free to sell in countries where no relevant patent exists.