Integrated 6mm allen key system with 12mm / 15mm hollow axle,with cover to keep tool in position. SPEC: 135mm SHIMANO® hub / Length 168mm / 12x1.75 W/i nut 142mm SHIMANO® hub / Length 171mm / M12x1.5 W/i nut 148mm SHIMANO® hub / Length 177mm / M12x1.5 W/i nut 150mm SHIMANO® hub / Length 183mm / M12x1.75 W/i nut 135mm SRAM® hub / Length 167mm / M12x1.75 W/o nut 142mm SRAM® hub / Length 174mm / M12x1.75 W/o nut 148mm SRAM® hub / Length 180mm / M12x1.75 W/o nut 150mm SRAM® hub / Length 182mm / M12x1.75 W/o nut OPTION: M12 x 1.0 THREAD / M15 x 1.5 / M14 x 1.5 Custom length thread design available 12mm / 15mm axle custom design available