Measure And Reduce the header rail. Pull the shower door shut and extend your tape measure from a person side to the opposite. Mark the size within the body header and use your hacksaw to cut it to measurement. Sleek down the raw edge using a steel file.[13] X Analysis https://www.deluxeshowerdoors.com/services/glass-shower-door-installation-in-needham-ma-deluxe-shower-doors/