It is the physical metal key that slides or clips into the key shell
Key details
It is not a full remote or smart key by itself.
Most modern versions are purely mechanical (no electronics)
Older versions (especially on some 2009–2018 models) may include a transponder chip so they can also start the engine.
The blade must be cut to match your vehicle’s locks
Mazda foldable insert to start shell is the outer plastic case of the fob.
The Mazda insert is the metal blade that goes inside that shell (or is released from it).