Specification: Product Name: Bicycle Guide Roller;  Material: 7075 High Strength Aluminum Alloy;  Type: Fit for 4/5/6 MM roller screw axis;  Structure: Ceramic bearing;  Size: 13T;  Weight: About 7.2g;  Color: Black/Red/Blue/Green/Gold;    Features: Suitable for all cycling applications, whether it is road, MTB, or triathlon, these pulley wheels will optimize your speed rear derailleur with reduced friction and extended lifetime.  Aluminum pulley wheels,weighing only astonishing 7.8g grams, these lightweight pulley wheels are fitted with ceramic bearings, which reduce friction and feature increased lifetime.  The aluminum alloy is very durable, and together with the pulley design, the set optimizes the overall performance of your derailleur. The removable design also makes the maintenance much easier.  For guide pulley, we use POM bearing rings instead of steel bearing rings, POM is an engineering thermoplastic used in precision parts requiring high stiffness, low friction, and excellent dimensional stability.    Package included: 1 x Bicycle Guide Roller;    Note: - Please allow 1-2mm differs due to manual measurement.  - Due to the different display and different light, the picture may not reflect the actual color of the item.  Thank for your understanding.