Quiet & Smooth: 2" Nylon garage door roller uses precision 13 ball bearings and nylon rollers to reduce garage noise by 75%. Durable Replacement Garage Rollers: Premium nylon housing and galvanized steel wheels with double wall reinforced bearing frame for maximum strength and lifetime durability. Durability: 6200Z bearings, verified test ratings exceeds 100,000 door open/close cycles at 150 lbs load Sealing Caps: Front and rear sealing caps prevent dirt and grime from penetrating the bearings Size & Package includes: 12 Pack garage door rollers,standard size for 2" (5.1cm) tracks, 4.78" (12.1cm) overall length with 4.25" (10.8cm) stem shaft, 0.43" (1.1cm) shaft diameter, 0.48" (1.22cm) thick wheel, 1.8" (4.6cm) wheel diameter