John Guest Push Fit is for the plumbing of Hot & Cold water services and central heating applications, including pressurized systems. These Speed-Fit Twist and Lock fittings have been designed for use with Copper Pipe, CPVC and PEX. Fittings indicate copper pipe ID. What not to do 1. Do not use damaged or seored pipe 2. Do not use hacksaw to cut pipe 3. Do not leave burrs on end of pipe 4. Do not forget to push the pipe fully into the fitting. Past both the collet (gripper) and the 0-ring. Twist and Lock Feature: Gives added security with greater compression on the o-ring, as pipe is locked in place.