Replacement Bobbins *12-PackBobbins are a replacement part for all Halkey Roberts type automatic inflators. They dissolve when immersed in water and cause the CO2 cylinder to inflate the PFD. All Mustang automatic inflatable PFDs come with cylinders and bobbins.Mustang Survival recommends annual maintenance and inspection of your PFD. For recreational use, bobbins should be replaced every three years to avoid inadvertent inflation.Configuration:The MA9210 is a master pack containing 12 individually packaged bobbins. The individual packages are available for purchase at your local Mustang Survival dealer.