Evaluate and Slice the header rail. Pull the shower door closed and lengthen your tape measure from one side to the other. Mark the dimensions over the frame header and make use of your hacksaw to chop it to size. Smooth down the raw edge using a metal file.[13] X https://www.deluxeshowerdoors.com/services/glass-shower-door-installation-in-needham-ma-deluxe-shower-doors/