The first few years that I got here to my hubby's place, his contract engineering business was booming. That was seven years ago before the economy tapered off. He used to order a wide variety of industrial products via phone and online such as nuts, hex cap screws, bolts, washers and such. The company where he used to order has a large selection of all kinds of industrial products that made it easy for him to design and build his engineering projects. They even sent him catalog on a regular basis free of charge.
My hubby used to design and build a lot of mechanical systems for industrial purposes. Aside from using industrial supplies that he ordered online and by phone, he also used a lot of off the shelf products like belts, pulleys, chains, sprockets and all kinds of miscellaneous hardware for the drive systems that made his machines go.