In 2014 TNG also offered GIANO-B to the scientific community, providing a near-infrared (NIR) cross-dispersed echelle spectrograph covering 0.97 − 2.45 µm at a resolution of 50000. The possibility of simultaneously using GIANO-B together with the HARPS-N spectrograph (GIARPS observing mode) has been particularly appealing especially for the search of exoplanets by means high precision radial velocities. Moreover, GIANO-B triggered the possibility to observe in the NIR the Sun as a star by means of LOCNES, a solar telescope that feeds the spectrograph by a bundle of NIR fibers, for study the activity of the Sun as a star in the NIR wavelength range and its impact on the radial velocity measurements. Both science cases, include high-precision radial-velocity studies down to 3 m/s which demand for specialized, highly accurate wavelength calibration techniques. In this paper we present a developed absorption gas-cell to enable high-precision wavelength calibration for GIANO-B as a modified model of the CRIRES+ Absorbing Cell. We also discuss the manufacturing difficulties and the new design of the vessel. Furthermore, the AIT and the commissioning of the cells is also reported.