Rear derailleur chain tensioner with aperture 10 mm (0.39 in) that keeps chain tension stable and delivers smooth gear changes, even on rough surfaces. Key benefits - Lightweight, portable and compact design for easy carrying and quick setup - Easy to install and operate, suitable for DIY maintenance - Maintains stable speed changes on rough terrain, reducing chain slip Material and build - Made of aluminum alloy for reliability and stability in diverse riding conditions Design and aesthetics - Stylish, elegant appearance that complements the bicycle without looking bulky Function and performance - Smooth speed change and reliable performance across different road conditions - Simple operation that suits both beginners and experienced riders Compatibility and use - Aperture size: 10 mm / 0.39 in 2-3 practical use scenarios - Off-road or mountain trail riding where terrain is irregular and chain tension often changes - City commuting with uneven pavement, potholes and frequent gear shifts - Long-distance rides where consistent chain tension helps maintain steady performance This chain tensioner provides a practical upgrade for riders who want dependable shifting, a clean look, and straightforward installation without compromising on performance.