The locking bolt, also called a door bolt, is the metal bar that, once thrown, comes out of the lock body and slides into a hole in the frame, holding the door in place.
It is one of the parts that physically keep an armoured front door shut.
In everyday language “locking bolt” and “door bolt” mean the same mechanism: a bar that slides and locks into a fixed point.
In an armoured door the locking bolts are made of steel and are the real holding points against anyone trying to force the door.
Locking bolt and door bolt: are they the same thing?
Yes, in everyday use locking bolt and door bolt are synonyms, even if the origin of the two words is different.
The door bolt is the more general term and means any bar that slides to block an opening, as the dead bolt entry on Wikipedia also explains.
The locking bolt is the everyday word, the one you use when you say “throw the bolt” before going to bed.
On a modern armoured door the locking bolts are not worked by hand one by one: they all come out together from the lock body when you turn the key or the handle.
The locking bolt in the armoured door
In an armoured front door the locking bolts are the steel bars that, driven by the lock, come out of the sides of the leaf and slide into the keeps in the frame.
Each locking bolt is a locking point: the more there are and the better they are spread out, the more evenly the door resists a push or a lever.
The locking bolts do not work only on the lock side. Serious doors have holding points on the hinge side too, so the door cannot be levered off from the side opposite the handle.
The material matters: a locking bolt in hardened steel resists cutting and bending far better than a simple bar of light metal.
Locking bolts and key turns: how many locking points do you need?
Here there is a common misunderstanding to clear up. More key turns does not mean more locking points.
In many modern armoured locks all the locking bolts already come out on the first turn of the key. The following turns do not add new points: they make the locking bolts travel further into the frame, increasing the hold against any attempt to force the door.
What makes the difference is therefore the quality and distribution of the locking points, not the number of turns you give the key.
To understand how the locking bolts fit into the wider picture of security, it helps to read the guide on armoured door locks.
The locking bolt and the security of the door
The locking bolt on its own is not enough to make a front door secure. It is one link in a chain that includes the lock, the cylinder, the defender, the frame and the fitting.
A sturdy locking bolt set into a weak frame is of little use, because an attacker would go for the weakest point of the whole. The real security of an armoured door is measured by its burglar resistance class, which assesses all these elements together with standardised break-in tests.
You can find the resistance classes and what they really mean explained in the article on armoured door burglar resistance classes.