The security door locks can be classified into three categories: A-class, B-class, and super-B-class according to the anti-theft level.
Class A locks are generally divided into three types, one is flat, and both sides can be inserted into the keyhole to open. The other is flat and semi-circular. This has two sides, one side and one side, one side is a glossy surface, and the other side is a marble slot. There is also a cross. These three A-class locks, in contrast, the flat semi-circle has good anti-theft performance, down to the plane double-sided, the worst anti-theft performance is the cross type.