Alumina, which is also known as Aluminum oxide, has a broad range of applications, especially in the ballistic industry, it can be used in hard armor plates in level III and IV.
These armor plates are made from alumina-based ceramics, in order to improve the strength of the ceramic material. This ceramic plate helps to protect the body with level III rating when it used inside of IIIA bulletproof vest.
It used in conjunction with your normal level IIIA bulletproof vest, and it can be easily inserted into 25x30cm pocket to provide level III ballistic protection. These ceramic plates are usually placed in the external 25x30cm / 10x12inch pockets of the bulletproof vest in the chest and back.
Even though most bulletproof vests are made of aramid, which usually have some level of protection as level IIIA against bullets as 9mm and .44 Magnum, these SAPI cut plates are meant to provide improved protection from high velocity rounds as rifle round for affordable price and without adding too much weight.
Fully rectangular plates usually cover a little more area than plates whose top edges has been cut off as on this SAPI cut shape. However, this SAPI cut armor plates offer a much better level of freedom of movement to anybody that is wearing them as users do not suffer from the discomforts associated with wearing a rectangular vest with uncomfortable edges.