1 13/16′ Nylon Roller, 11 Ball Bearing. White nylon tire. Bulged shoulder, Zinc plated stem. Rated 75lb; 15,000 cycles of a 12′ door (Better- roller that will make your garage door smooth and quiet) Anytime your door is operating smoother and quieter it means that there is less friction. Your opener will last much longer when it is not dragging your door up or dragging the door down. You are also increasing the life of your garage door by taking stress off of the top panel where the opener pushes and pulls.
The purpose of the 7′ stem is if you have 2 hinges side by side for the stem to go through. This is usually used on really wide, heavy doors that required a wind load kit.