Hylomar underhead sealants are designed to replace conventional mechanical forms of underhead sealing such as copper, aluminium, rubber or composite washers. When assembled the underhead sealant is forced into the gap between the head of the bolt and the component assembly to form a seal. The underhead sealant has good chemical and moisture resistance to form both a fluid and an environmental seal. A licenced application process is used to form the precise bead dimensions ensuring no excess product is applied to the component. The process is suitable for application to bolts, plugs, rivet and rivnuts.