Inactive Leaf Second opening leaf of a pair of doors. It usually houses the strike.

Indicator A device that shows the state of the locking mechanism, locked or unlocked. Used for toilet cubicles, etc

Indirect Key Coding A code marked on a key or lock which requires reference to another series of codes to disclose the key cuts for creating a workable key.

Individually Keyed See Keyed To Differ.

Inset The distance from the face of the door to the face of the jamb.

Insulation Material for obstructing passage of sound or heat from one surface to another.

Interchangeable Core System A cylinder which can be removed from its lock by a special control key.

Interlocking Joint A joint formed between sheet metal parts by engaging their edges, which have been pre-formed to provide a continuous splice.

Ironmongery See Door Hardware.