These round or square products made of ferromagnetic metals are called steel(metal) discs and plates, and their surfaces can be galvanized or nickel plated. Steel metal disc(plate) of different shapes play an important role in the application of permanent magnets. Steel metal disc and plates are usually used with magnet disc or plate produce closures and increase the magnetic force. Compared with using two magnets to attract together, steel (metal) disc is a cheaper option, one of the magnets can be by a ferromagnetic steel(metal) discs and plates.
The same as magnets, steel disc can be also made with countersunk hole or self-adhesive backed. We can supply different sized countersunk steel discs and adhesive backed steel discs.
All the round steel(metal) discs are made of ferromagnetic steel, which can be used for permanent magnet. You can use a round ferromagnetic steel disc to stronger your magnet. Nickel or zinc plated steel (metal) discs are regular supplied with size range from 10mm to 60mm.
Steel(metal) discs with countersunk hole can be firmly fixed onto any surface, they are usually used together with magnets. You can used countersunk steel disc in stead of magnet in door closure system to save cost. M3,M4 screw holes are available for the steel metal discs with countersunk hoes. 
The ferromagnetic steel discs are backed with high-adhesion 3M self-adhesive or foam adhesive. With adhesive backed steel(metal) discs, you can attach a magnet onto non-metal surface. Our adhesive steel discs are provide with various size range from 10mm to 60mm.
