ZTTO 11T MTB Bicycle Rear Derailleur Jockey Wheel Ceramic Bearing Pulley Road Bike Guide Roller Idler 4mm 5mm 6mm All the results of the simulations and the experimentations indicated that the ceramic ball bearings' performances are very good, especially in the low load and high-speed environment. Suitable for all Cycle applications, whether it is road, MTB, or triathlon, these pulley wheels will optimize your speed rear derailleur with reduced friction and extended lifetime. Features: Suitable for all Cycle applications, whether it is road, MTB, or triathlon, these pulley wheels will optimize your speed rear derailleur with reduced friction and extended lifetime. Being the fastest spinning bearings on your bike, an upgrade with our high-performance pulley wheels are an effective way to save energy or ride faster. Weighing only astonishing 7.7g grams, these lightweight pulley wheels are fitted with hybrid ceramic bearings, which reduce friction and feature increased lifetime. The aluminum alloy is very practical, and together with the pulley design, the set optimizes the overall performance of your derailleur. The removable design also makes the maintenance much easier. They are also resistant to water and salty environment and they will never need lubrication or getting rusty. For guide pulley, we use POM bearing rings instead of steel bearing rings, POM is an engineered thermoplastic used in the parts requiring high stiffness, low friction, and excellent dimensional stability. Specifications: Brand: ZTTO Material: aluminium alloy Color: red, black, blue, gold, titanium (optional) Fit for: 4/5/6 MM roller screw axis Size: 11T Item weight: 7.7g / 0.27ounce Package size: 100 * 50 * 50mm / 3.9 * 2.0 * 2.0in Package weight: 19g / 0.7ounce Package List: 1 * Bicycle Jockey Wheel