Joining components

A component 10 for joining to a further component 11 in a preselected relative orientation, contacting an interface surface 111 of the further component when joined. The component comprises a surface 101 facing the interface surface when the components are joined, a plurality of recesses 12a-c formed in the surface, and a plurality of spacer elements 13a-c. Each recess has a preselected orientation relative to the component. Each spacer element comprises a contact surface 131a-c contacting the interface surface when the components are joined. Each spacer element is disposed in one of the recesses such that the orientation of a given contact surface is defined by the orientation of the corresponding recess. Optionally, the surface is curved and convex (see figure 3) and the interface surface is flat. Spacers may be cylindrical and recesses may comprise counterbores or sockets. Components may include aircraft wing, interface plate or engine mounting