This shim fits as shown to trigger the Z axis end stop sooner to account for the thickness of the PRINTinZ flexible printer plate. All plates are slightly different in thickness, but 4.5mm is the average. Use the bed leveling screws as needed to adjust from there. You can get the PRINTinZ plate at www.printinz.com. Thanks to salbemerson and mclarke for the original designs. This is just a modification for the thicker PRINTinZ Plate release in July of 2015 (originally called the Zebra Plate).