What is the pad zero?

[MadModder]

Some of my footprints have a pad number 0 (zero), and it's name is "free-0". It sits exactly in the middle of the footprint on mechanical layer 15, has a size of 20mil, and has no other properties.
What is it good for?
It isn't created when using the footprint wizard.
No schematic symbol I've seen has a pin 0 hidden.
I remember Dave said in a video a long time ago that deleting pad number zero is a beginners mistake.

[T3sl4co1l]

Your footprints?  You made 'em, you should know..?

Sounds like it might be intended to show up on the pick-and-place file as a part centroid marker.

Pads on graphical layers tend to be a mistake rather than intentional; imported AutoCAD can make a lot of pads for example.

Personally, I use pad 0 for no-connects, e.g. unplated holes for mechanical mounting.  Any name will match up with any schematic pin name so this is just convention.  I never place pads on non-electrical layers.

Tim

[MadModder]

No I did not place them, and not a single schematic pin has the number zero, anywhere.
First I thought it is because I imported libraries from Orcad years ago, but the footprints in question are made after I started using Altium.
Very strange.
Those are the first footprints I made in Altium though, 4 years ago. I may have done something wacky. 

[mengfei]

think those are used in some machines to align them in the PAP machine but now machines are more intelligent & accurate.
usually those are in the Mechanical Layer together with some other outlines in that layer that when you turn them all on it even make s you more confusing
Some Zer0 pads are for mounting brackets soldered on PCB but have no electrical or sometime GND connections

[Psi]

Some of my footprints have a pad number 0 (zero), and it's name is "free-0". It sits exactly in the middle of the footprint on mechanical layer 15, has a size of 20mil, and has no other properties.
What is it good for?
It isn't created when using the footprint wizard.
No schematic symbol I've seen has a pin 0 hidden.

A pad is not always an electrical pad, the same as silkscreen tracks are tracks, but not electrical tracks.
The layer they are on governs what they are used for.

If this pad is on mechanical 15 layer and is always in the center of the part then i agree with mengfei, it's likely something related to pick-n-place alignment.

[Pseudobyte]

Some people like to include centroid markers on mechanical layers. The fact that it is a pad and not a primitive feature is likely a result of the conversion from OrCAD to Altium. You generally keep the centroid on it's own layer so that when you generate your documentation you can turn the centroid markers on and off depending on the drawing view you are trying to create.