This 4 in. Nylon Garage Door Roller (individually) is the ultimate roller to quiet and prolong the life expectancy of your garage door. With a caged 6200Z 10-ball bearing that is rated at 100,000 door open/close cycles, this roller is 10x stronger than the average of 10,000 door cycles for other rollers. The ball-bearing nylon wheel is 75% quieter than steel and non-bearing rollers. The 6200Z bearing protects the inner ball bearing from dirt and grime over time, resulting in the smoother opening / closing of your garage door.