What's the difference between a petty officer and a sergeant major?

A master sergeant is a rank of sergeant.

Non-commissioned officers include corporal, sergeant, staff sergeant, master sergeant four, master sergeant three, master sergeant two and master sergeant one.

The rank of noncommissioned officers from low to high is corporal (a cross rifle decorated with golden and semi-round ears of wheat and a thin folding rod),

Sergeant (cross rifle, decorated with gold and half a circle of ears of wheat, plus a thick folding rod),

Staff sergeant (cross rifle decorated with golden and semi-circular ears of wheat, a thick folding rod and a thin folding rod),

Fourth-class master sergeant (golden cross rifle decorated with golden semi-round ears of wheat and two thick folding bars),

Master Sergeant III (cross rifle decorated with half a circle of wheat ears, two thick folding bars and one thin folding bar),

Master Sergeant II (cross rifle with golden ears and three thick folding bars),

First-class master sergeant (cross rifle, decorated with golden semi-round ears of wheat, three thick folding rods and one thin folding rod).

Conscripts are divided into private soldiers and superior soldiers. The two-fold bar is a superior soldier; The crappy bar is a private.