I'm in the process of adding limit switches to my Shapeoko. Limit switches are nice because they give you two things: 1) They give you some added protection against driving a carriage off the end of your machine. 2) They give you the ability to set up an auto-homing routine. Auto-homing can be very helpful when you're doing a lot of repeat cutting against a fixed jig. I found this 5-Pack of limit switches on Amazon for less than $5. That provides more than enough limit switches to set up an auto-zeroing system. The mounts nestle inside the makerslide. The two holes should be tapped for M5 screws and bolted to the end-plates. This document describes how to connect limit switches to grbl. Here's a video of the switches in action! Edit Small change: added a third hole to allow for mounting on the y-axis end-plate.Tap the two holes for M5 screws. Then set inside the makerslide grooves and bolt to the Shapeoko end-plates.