Plays an important role in the early step of spermatogenesis. Hydrolysis of terminal, non-reducing alpha-D-mannose residues in alpha-D-mannosides. Binds 1 zinc ion per subunit. Mainly expressed in the narrow region between the caput and corpus epididymis. Specifically expressed in type A spermatogonia at stages IX-XI of spermatogenesis. Detected there until the cell developed into type B spermatogonia. Belongs to the glycosyl hydrolase 38 family.