Question zero plate

This may have been discussed in the past but the search function didn't turn up anything.
There's a 3.5 mm socket sticking out the back of my system which I think is for the touch probe. I'd like to use it to make a zero plate.
Has anyone done this? Any pointers?

NIce question

However we are no physics who can determine what machine you own or what the configuration is.
So next time give valid information before you ask "in the blind" else you never get an answer you want.

Well, it is an input which can be read by the software driving the CNC. Does not matter what exact device you attach to it, it only needs to be a switch and it needs to be setup correctly in the CNC software.

So, SC has two devices which might be connected to it: the tool length 'sensor' and the 3D touch probe.

The difference between those two and a zero plate is, that a zero plate is by design a closing switch - one wire is connected to the plate, one to the endmill and if endmill touches the plate the circuit is closed. For the other sensors the preferred design is as opening switch. Reason is, that an opening switch would be seen as triggered (and machine is stopped) in case there is an electrical issue. Like a loose connection. This protects the machine from driving the endmill / touch probe into something only because of a loose connection.

So, if you want to have both kind of sensors, you have to switch configuration in the software before using or you change the opening switched devices to closing switch devices. Then you even can attach all devices in parallel (only for closing switch devices) and work with the same setting in the CNC control software. But in that case you loose the protection from loose connections, so you better closely watch the measuring process and hit emergency stop in case of failure due to a loose connection.