Box One™ Chain Tensioners are extruded then CNC-machined from 7075 aluminum for an optimal balance of strength & weight. A minimalist design adds style while reducing their overall mass. Laser-etched graphics that include wheel position guides & two 10mm mounting holes ensure perfect adjustability on most frames every time you remove & replace your wheel. When used properly, Box One tensioners will protect your frame dropouts & 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 & leave the 15-inch breaker bar in your toolbox.