What are the three main features of mass production?

Machine tools, specialization, and interchangeable parts.
Machine tools help with the assembly line work, making each part easier to make and more accurate.
Each person at each station is specialized in that one piece. They know how to make it right and are able to check for errors much better than if someone was checking a whole item.
Because of each part being made the exact same, the parts are interchangeable so that someone can take all the parts to create the finalized product. Also, if some part breaks, a replacement can be readily available.