As part of your modular technical diving rig the backplate creates the stability for the entire set up. Backplates are good for single and twin setups with all the mounting points for a range of webbing harnesses, wings and bolts. Down the spine you have holes and slots for mounting cylinders and your wing, up around the shoulders and waist are slots for your harness and all around the edges are mounts for accessories like butt plates and inflation cylinders. Steel Backplates are strong and heavy where you need extra weight to make you neutral so you can take some lead off your weightbelt. Aluminium Backplates are much lighter and corrosion resistant so better for travel and when you don't need the extra weight to get down.