Exoglycosidase that cleaves the single beta-linked mannose residue from the non-reducing end of beta-mannosidic oligosaccharides of various complexity and length. Involved in the degradation of polymeric mannan and galactomannan (By similarity). Hydrolysis of terminal, non-reducing beta-D-mannose residues in beta-D-mannosides. Glycan metabolism; N-glycan degradation. Homodimer. Belongs to the glycosyl hydrolase 2 family. Beta-mannosidase A subfamily.