Your cylinders will become more bouyant as the dive progresses (more with aluminium than steels), this bungee d-ring replaces a fixed or stainless steel d-ring. It slides along the 2 inch webbing, this allows you to accurately correct the trim of your sidemount mount cylinders throughout your dive. The cylinders shown in video are aluminium 80's. For more information visit www.sidemountscubadiving.com.