Flat pad, flat pad is mainly stamped out with iron plate, the shape is generally a flat washer, with a hole in the middle.There is a calculation formula in the “Standard Fastener Quality Encyclopedia” published by China Standards Press. The formula is: Weight of one thousand pieces m=0.00785×{3.1416/4×washer height× [Square of outer circle diameter－square of inner hole diameter]}

The role of flat pads：

1. Increase the contact area between the screw and the machine.

2. Eliminate the damage to the surface of the machine by the spring pad when removing the screws.When used, it must be a spring pad and a flat pad. The flat pad is next to the surface of the machine, and the spring pad is between the flat pad and the nut.

3. Flat washers are usually thin pieces of various shapes, which are used to reduce friction, prevent leakage, isolate, prevent loosening or disperse pressure. Many materials and structures have such components, which are used to perform various similar functions.Limited by the material and technology of threaded fasteners, the support surface of bolts and other fasteners is not large, so in order to reduce the compressive stress of the bearing surface and protect the surface of the connected member, washers are used.　In order to prevent the loosening of the connecting pair, anti-loosening spring washers, multi-toothed lock washers, round nut stop washers, and saddle-shaped, wave-shaped, and tapered elastic washers are used.