These instructions apply both to traditional fittings and to fittings with the advanced back-ferrule geometry. Further tighten the nut until the tube will not turn by hand or move axially in. Proper installation is critical for achieving a leak-free, vibration-resistant, and reusable seal with ferrule fittings. At Perfect Engineers, our PE-LOCK double ferrule compression fittings are precision-engineered to offer reliable connections—but only when installed correctly. Interested in more information about our process or products?The purpose of this guide is to provide comprehensive, step-by-step instructions for installing ferrule fittings. “Measure the hose wall, then use the chart.