Box One™ Chain Tensioners are extruded then CNC-machined from 7075 aluminum for an optimal balance of strength and weight. A minimalist design adds style while reducing their overall mass. Laser-etched graphics include wheel position guides and two 10mm mounting holes with 15mm of adjustment to ensure perfect adjustability. Fits most frames every time you remove and replace your wheel. When used correctly, Box One tensioners will protect your frame dropouts and hold your rear wheel in place. Keep in mind. However, they aren’t indestructible (neither are your dropouts). Install these lightweight chain tensioners with care and leave the 15-inch breaker bar in your toolbox.