What are the main differences (except for the obvious, one is round one is square) between the round pin headers and the square ones?
Or differently asked: Why would someone choose round pin headers over the square ones (or the other way around)?
Round pin headers:
Square pin headers:
Best Answer
The round pin headers (also known as "machine pin headers") typically provide a more secure fit, with more contact surface area between the pins and sockets. They are often used in applications where vibration is a problem.
They're not used universally, because the machining process makes them significantly more expensive to manufacture than the square pins. Also note that the square pin typically won't fit into a round socket, and round pins going into square sockets can have problems maintaining position (or even contact).