INSERT FOR A WIND TURBINE BLADE ROOT

An insert (105) for a wind turbine blade root. The insert (105) has a bushing (40) and an outer surface with circumferential annular grooves (68). A transition layer 5 (102) is built up around the bushing (40). The transition layer (102) has fibrous material sheet layers and filamentary material windings (80) in the grooves which alternate with fibrous plies (98) covering the grooves (68). Each fibrous ply (98) is anchored into the grooves (68) by the windings (80). Fibrous battens (148) are fitted around the transition layer (102) to form an insert body (108). Each batten (148) 10 has a deltoid cross-section so that the battens give the insert a quadrilateral or trapezoidal cross-section.