A comprehensive set of research and development activities has been carried out at Consorzio RFX regarding the construction of the grids for the ITER neutral beam injectors, in order to validate the proposed manufacturing methodologies, to further develop the details of the engineering design, and to adapt existing production techniques to the specific case. In the framework of this research and development program, two multichannel prototypes have been designed and manufactured. These prototypes feature all the possible manufacturing issues of the source for production of ion of deuterium extracted from RF plasma (SPIDER) grids. In fact, they reproduce the geometry of the extraction grid (EG) for SPIDER by having the same thickness, same cooling channels, same distributors, same aperture shape, and same slots for the magnets of an EG segment. The differences from an actual EG segment regard only the dimensions, i.e., reduced width (one fourth) and height (one half). The construction and testing of these prototypes are here described in detail.