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. Releases the terminal mannose residue from mannobiose and mannotriose, as well as from galactosyl-mannobiose (GM2), galactosyl-mannotriose (GM3) and di-galactosyl-mannopentaose (G2M5). Hydrolysis of terminal, non-reducing beta-D-mannose residues in beta-D-mannosides. kcat is 4048 min(-1) with p-nitrophenyl-beta-mannopyranoside as substrate. Optimum pH is 2.5-5. Optimum temperature is 70 degrees Celsius. Glycan metabolism; N-glycan degradation. Homodimer. N-glycosylated. Belongs to the glycosyl hydrolase 2 family. Beta-mannosidase A subfamily.