These metal plates come in a set of two, one rectangular plate, and one circular.
 
Dimensions:
 
Rectangular Plate - 65mm * 45mm
Circular Plate - 45mm Diameter 
 
These metal plates are ferromagnetic, meaning that they by themselves are not magnetic, but are magnetic when introduced to a magnetic item like magnetic car mounts.
Applied with the strong adhesive sticker on the back, can stick on your phone back firmly and securely
Without sharp edges would not damage your fingers and smartphone
Made of premium stainless iron, durable and wear-resistant