A kit of parts for forming an aerofoil structure including a torsion box for use in attaching a fixed leading or trailing edge structure to the torsion box, and a fixed leading or trailing edge structure attachable to the torsion box. The torsion box includes a first mounting feature. The fixed leading or trailing edge structure includes a second mounting feature configured to engage with the first mounting feature. The first mounting feature and the second mounting feature are mutually configured to permit the first and second mounting features to be moved into engagement with each other along a first direction, and to prevent relative movement of the first and second mounting features along a second direction when the first and second mounting features are engaged with each other.