The blade root is usually circular in cross section to connect to the pitch bearing in the hub. The blades are fixed to the hub via a bolted connection that allows them to be removed. Most blade roots consist of a thick solid laminate with studs or T-bolts either screwed or bonded in. The girder structure (or box section) of the load carrying spar must be joined to the cylindrical laminate at the root. Normally this is done by incorporating a smooth curved transition area. Care must be taken during the curing of the composite structure as the high thickness in the laminate sections could lead to a build up of high exothermic temperatures. Many manufacturers therefore make the root as a separate component and bond it into the structure. The bonding of this joint is critical and concentration of stress in this area must be avoided. This is a critical area of the blade, requiring a very high quality of laminate. Hexcel has an optimized range of prepregs and other fiber-reinforced composites for root construction.