Exoglycosidase that cleaves the single beta-linked mannose residue from the non-reducing end of beta-mannosidic oligosaccharides of various complexity and length. Prefers mannobiose over mannotriose and has no activity against polymeric mannan. Is also severely restricted by galactosyl substitutions at the +1 subsite (By similarity). Hydrolysis of terminal, non-reducing beta-D-mannose residues in beta-D-mannosides. Glycan metabolism; N-glycan degradation. In contrast to clade A beta-mannosidases, which are likely secreted, clade B proteins appear to be intracellular. Belongs to the glycosyl hydrolase 2 family. Beta-mannosidase B subfamily.