The 3rd Fermi catalogue of Hard Fermi-LAT Sources (3FHL), which detected 1556 sources above 10 GeV, provides an important resource for finding new candidate TeV sources for follow-up observations with the H.E.S.S. telescopes. To search for potential TeV emitting extragalactic sources, we observed a sample of five 3FHL sources classified as Blazars of unknown type (BCU) and two 3FHL sources without associations at other wavelengths with the SAAO 1.9-m telescope. The observations were performed during February 2017, with the SpUpNIC spectrograph on the 1.9-m telescope. Possible counterparts for the unassociated sources were determined by cross-matching objects using archival multi-wavelength data from Radio, Infrared and X-ray catalogues. Classifications were obtained for all the observed BCUs and redshifts were determined for two of them. Redshift measurements were obtained for the optical candidates of both the unassociated sources observed. Further analysis is necessary to confirm their association to the 3FHL γ-ray sources.