A "sewing bobbin with gears or cogs on the ends" isn't a standard sewing machine part; instead, a bobbin is a small spool that holds the bottom thread, and the "gears or cogs" likely refer to the ridges on the bobbin's ends that keep thread in place, or external gears driving the machine's various mechanisms like the hook or feed dogs. Its core function is to provide the bobbin thread that interlocks with the needle's top thread to form a stitch. These bobbins can be used with both gear driven internal mechanisms or standard sewing machines. The bobbin cogs or gears are used for the internal mechanism of your sewing machine or they can be used on normal sewing machine.