Perfect for a Z sync mod on a CR10S Pro. You need to purchase 2x GT2-6 Timing Belt Pulley 20T (Inner Bore 8mm) and one GT2-6mm Timing Belt Loop 760mm. On the CR10S PRO the X gantry/axis will sag a little bit on the left side when you turn off the printer and remove power to the stepper motor because of the weight of the X stepper motor and the extruder stepper motor. So from time to time you will have to re-adjust the X axis otherwise it will be very hard to get a good first layer. With this simple mod both lead screws are kept in sync by the belt even when the power is turned off on the printer.