A door chain, security chain, or security door chain or chain door interviewer consists of a small chain attached to the door frame, which attaches to a track on the door for security purposes. It is a type of lock that is often used along with other types of locks to secure a door.
D locks are more secure than portable chains and often have better sold secure ratings. Normally D locks cost the same if not less than portable chains. D locks are highly practical and can easily be stored in a rucksack or through a belt loop
Industrial chain is rated by grades; the higher the grade number, the more steel alloying elements it contains and the more resistant it is to the variety of loads a chain encounters, especially in tension. Grades 70, 80, and 100 are among the hardest and toughest available
Metal type: The strongest metals for chains are gold and platinum. White gold with rhodium plating can have added strength. Sterling silver chains are also pretty strong, but they require more upkeep to prevent tarnish.
Door chains give you some protection when you need to open the door. More importantly, they give you a few vital seconds whereby you can slam the door shut should an intruder try to force their way in. For a small investment, a door chain adds an additional layer of home safety and security.
Grade 120 chain exhibits the strongest tensile strength of all steel alloy chains and is used for exceptionally heavy overhead lifting
Lock-chains. Are chains used to lock the wheels of field- and siege-carriages, or to prevent them from turning. For siege-carriages the chain has a shoe at the end, which goes under the wheel and lifts it from the ground. In field-carriages the chain is passed around one of the felloes and secured to itself by a key.
Deadbolt door locks are the most secure type of key lock and are usually used on a home's exterior door. Available in single- and double-cylinder styles, deadbolts are rated according to their strength from Grade 1 to Grade 3. A Grade 1 is the highest grade and provides the most security.