A kit of parts for forming an aerofoil assembly, the kit of parts comprising: a torsion box structure comprising a first attachment point and a second attachment point, the first and second attachment points being separated from each other along a separation axis, and a fixed leading or trailing edge structure comprising corresponding first and second attachment points for attaching to the first and second attachment points of the torsion box structure, the first and second attachment points being separated from each other along a separation axis, wherein a first structure of the torsion box structure and the fixed leading or trailing edge structure comprises: - a slidably mounted abutment piece slidable along a slide path (343, 344) extending in a direction parallel to the separation axis of the first structure, and - a fixing mechanism for fixing the slidably mounted abutment piece in a chosen location on the slide path, wherein a second structure of the torsion box structure and the fixed leading or trailing edge structure comprises a corresponding abutment feature, for abutting against the slidably mounted abutment piece of the first structure, the abutment feature comprising a first abutment surface facing in a direction parallel to the separation axis of the second structure, such that, in use, the slidably mounted abutment piece of the first structure can be slid to abut the first abutment surface of the second structure and be fixed in that location by the fixing mechanism, to prevent relative movement of the first and second structures in the separation axis, characterised in that the slide path (343, 344) also extends in a second direction orthogonal to the separation axis and wherein the slide path (343,344) may extend in a third direction orthogonal to the separation axis and second direction. a torsion box structure comprising a first attachment point and a second attachment point, the first and second attachment points being separated from each other along a separation axis, and a fixed leading or trailing edge structure comprising corresponding first and second attachment points for attaching to the first and second attachment points of the torsion box structure, the first and second attachment points being separated from each other along a separation axis, wherein a first structure of the torsion box structure and the fixed leading or trailing edge structure comprises: - a slidably mounted abutment piece slidable along a slide path (343, 344) extending in a direction parallel to the separation axis of the first structure, and - a fixing mechanism for fixing the slidably mounted abutment piece in a chosen location on the slide path, - a slidably mounted abutment piece slidable along a slide path (343, 344) extending in a direction parallel to the separation axis of the first structure, and - a fixing mechanism for fixing the slidably mounted abutment piece in a chosen location on the slide path, wherein a second structure of the torsion box structure and the fixed leading or trailing edge structure comprises a corresponding abutment feature, for abutting against the slidably mounted abutment piece of the first structure, the abutment feature comprising a first abutment surface facing in a direction parallel to the separation axis of the second structure, such that, in use, the slidably mounted abutment piece of the first structure can be slid to abut the first abutment surface of the second structure and be fixed in that location by the fixing mechanism, to prevent relative movement of the first and second structures in the separation axis, characterised in that the slide path (343, 344) also extends in a second direction orthogonal to the separation axis and wherein the slide path (343,344) may extend in a third direction orthogonal to the separation axis and second direction.