A knob is the rounded gripping element, often spherical or “egg-shaped”, fitted to a door so you can pull it open towards you.
Unlike a handle, a knob does not press down: you take hold of it and, depending on the type, either pull or turn it.
On armoured doors the knob plays a role that goes beyond looks: it is a security choice, because on the outside it stops anyone from opening the door without the key. You can find its definition, etymology included, in the Collins English Dictionary.
Fixed knob and turning knob
The knob on an armoured door comes in two versions, and the difference matters.
A fixed knob is anchored to the leaf and does not move. It is almost always fitted on the outside of an armoured door: it only serves to pull the door, while to get in you have to use the key.
A turning knob rotates and, in some systems, operates the inner mechanisms of the lock. It is found more often on internal doors or in specific set-ups.
The rule of thumb is simple: fixed outside for security, handle inside for convenience.
Knob or handle: the difference
A knob and a handle do the same gripping job, but they behave differently. A handle presses down and, acting on the latch, opens the door in one movement. A fixed knob does not: it simply gives you something to grip and pull.
On an armoured door this difference becomes protection. With a fixed knob on the outside, an intruder has no lever to press down and cannot open the leaf: the only way in is the key in the cylinder.
On the inside, instead, you fit a handle or a turning knob, because there what counts is being able to get out quickly.
Why the outside knob on an armoured door is fixed
The fixed outside knob is one of the small details that raise the security of a front door. It takes a mechanical hold away from the burglar and makes any attempt to work the opening from outside pointless.
It follows the same principle as the rest of the door: every component, from the knob to the defender, works to leave the burglar one closed route only. You can find the full picture in the article on how an armoured door is made.
Frequently asked questions
A handle presses down and opens the door by acting on the latch, whereas a fixed knob only gives you something to grip and pull and opens nothing. That is why a knob is preferred on the outside of an armoured door: you get in only with the key.
For security. A fixed knob gives a burglar no lever to operate, so from outside the door opens only with the key. On the inside a handle is used instead, which is more convenient for getting out.
It depends on where it goes. On the outside of a front door you choose a fixed knob for security, while a turning knob makes sense where you need to operate a mechanism, such as on some internal doors or specific systems.