I made this for my X-carve and it works nicely. A did a few modifications:
On the cover, I removed the printed shaft and added a slot to insert a 1/8 shaft (I mostly carve with 1/8 tools).
For the probe itself, I grinded down a 10-24 screw because the z-axis on the x-carve is fairly limited.
I used stainless steel shoulder screws to prevent corrosion from interfering with the contacts. I'm not sure if that really matters, but I read that from some other probe designs.
The x-controller doesn't have easily accessible 5v, so I used a different circuit built around a pnp transistor (2n3906). This lets me use the same barrel plug for the probe without changing any settings on the cnc itself. The circuit is attached.