The answer is as simple as difficult. As a rule you will hardly be able to do this at first sight, because they look the same for the laity. They are heavy, made of metal and all shine. The only option you have as a final customer is not to get rid of any scrap, is to inform the manufacturer which materials were used. Try this for a lot of fun in the Far East. However, you do not count to this group of people if you read this.
I was especially attentive to the company Metalltechnik Kühne (Steeltoyz), because I wanted to know what had gone wrong with my first Ball stretcher and how I can prevent that I again throw a lot of money out the window.
Steeltoyz reveals everywhere that they do not buy the Ball stretcher somewhere, make label on it and ready, but in their own manufactory itself. The steel used for production is medical stainless steel, which is well tolerated by allergic persons. If you have questions, Mr. Kühne will be glad to answer you and is a competent contact person, especially in the implementation of special requests. The fact that the production in Germany and the use of high-quality material against foreign no-name products naturally has a higher final price effects is understandable, but you also have a precise and clean finished product of the highest possible compatible material and can in case of problems the manufacturer itself to contact.