How can you tell the difference between a 6 iron and a 9 iron?

Answer 1

Simply by the number on the bottom. But apart from that, the 6 iron has a more square face at address, whereas the 9 iron is a lot more open. The 6 iron shaft is also longer than the 9 iron.

Answer 2

The angle of the head is different. Some are for hitting the ball further, while some are to get more elevation on the ball.

Answer

Yup... the smaller the number is, the more closed the face is and the farther and lower it goes. The higher number is the more open the face is, the higher but not farther the ball goes. It all has to do with an angle.