Taiwan MARKONE (Markham Wang) sleeve, made of high quality chrome-molybdenum steel forged CR-MO, senior alloy steel, more durable. Exceptional arc angles designed to make sets of head and nut contact surface for the side contacts: 15% increase in torque to make it easier to tighten or nut open, increasing the service life nut can effectively reduce the nut corners worn, operation is not slipping, more security. manganese phosphate surface treatment, product appearance, anti-corrosion, easy raw rust and prolong sleeve life. widely used in mining, metallurgy, shipbuilding, automotive and other industries heavy machinery repair and disassembly of large screws used.