National 2" Inch 13 Ball Nylon Garage Door Rollers with 4" Stem (Pack of 12) A quantity of 12 -- 13 ball nylon garage door rollers Shaft length: approx. 4 inch Roller diameter: 1.75 inch for 2 inch track Shaft diameter: 7/16 inch 13 ball bearing rating: 125lbs per roller @ 20, 000 cycles 12' door