If you want assist measuring the centerline radius of the existing elbow, it's best to speak to an elbow manufacturing expert to make sure you get the correct measurements and the most beneficial Answer for your preferences. Pipe fitter teaching, metal fitter training, piping and structural fitter fabricator instruction tips https://www.malleableiron-pipefitting.com/industry-knowledge/how-to-find-elbow-center-of-pipe.html