Line of Linked Metal Securing a Front Portal

This page is the CodyCross answer for the clue below from Train Travel, Group 714, Puzzle 2 (Freight Service).

Question is: Line of Linked Metal Securing a Front Portal

and the answer is: DOORCHAIN

Word Meaning:

DOOR CHAIN — A device that allows a door to be partially opened from the inside, whilst preventing it from being fully opened from the outside.

Definitions from Wiktionary.