The B2-20 part of LIAN DUNG is a four-digit, non-returnable screw. It is made from stainless steel, and has four-winged flange edges which can be used for easy tightening and loosening of the screw. The screw is also fitted with a head that has three holes in it to allow for better torque control. The screw is ideal for use in a variety of applications, including computers, automotive, and electronics where easy, secure fastening and control is necessary.