This special edition High-Quality Black Linear Bearing – MGN7H is a tiny and lightweight rail slide block suitable for miniature equipment. This is most often used in 3d Printing, CNC Machining, Robotics, Measuring Equipment and Other Machinery. Along with the MGN7 Rail, this block offers high rigidity and precision accuracy. Specifications: All metallic components of the Block and Rolling Balls are made from chrome steel Arch contact design offers high rigidity and precision accuracy Steel Balls held captive by a retainer Sustains loads from all directions Uses a Rolling Circulation System Additional Information: Leave the Block Support Rail that comes with the packaging in the block until installation in order to avoid the Steel Balls from escaping the retainer. When installing the block onto the rail, use the rail to push the Support Rail out of the block, this ensures the Steel Balls are under tension and have contact with a rail at all times. Over Tightening of Rail Mounting Bolts will seriously affect the accuracy and function of the Block.