SparkFun's Description of the Shapeoko Touch Probe
The Touch Probe from Carbide 3D is a small accessory piece for your Shapeoko CNC machine meant to assist in finding the edges, or datums of the part you are milling. This part is an active probe, and when contacted to ground, communicates its position to the Carbide Motion program to help you fabricate easier.
Carbide Motion supports the 4 different types of probing: XYZ (otherwise known as corner probing), X (to find the left edge of your material), Y (to find the front edge of your material), and Z (to find the top of your material). All instructions and software support material can be found in the Documents tab above.
Note: The Shapeoko Touch Probe is only supported in Carbide Motion 4 and GRBL 1.1. This is only a software and firmware change, so no new hardware is required.