The sleeve (ferrule) in these fittings is made of rubber instead of metal, so it cushions the tubing and absorbs vibration while creating a tight seal. Fittings are also known as flareless fittings. They are zinc-plated steel for fair corrosion resistance.BSPP male threads have a gasket and washer to prevent leaks.90° elbows with external hex drive allow you to tighten from the top or bottom, which permits easy adjustments in tight spaces.