A process and device for mounting a sub-assembly that includes at least one coating product spray on a mobile part of a robot. The method includes:--engaging a support fast with the mobile part in a ring connected to the sub-assembly;--rotating this ring with respect to this support by bringing first projections provided on the periphery of the ring opposite second projections provided on the periphery of this support; and--displacing a bearing plate, connected to the mobile part, in the direction of this sub-assembly, until the plate exerts a bearing effort on the sub-assembly, the bearing effort being transmitted to the ring, with the result that the first and second projections are brought into mutual engagement. The device includes a ring connected to the sub-assembly and provided with first projections and a support, fast with the mobile part and provided with second projections, while a bearing plate borne by the mobile part is adapted to be displaced with respect to this support, the first and second projections being adapted to be brought into mutual engagement.