You are looking at a Scott Atwater antique outboard motor propeller.  This a Michigan propeller made Scott Atwater that has the Michigan part number SAC70 stamped in it.  This will fit all the 1955 to 1958 30hp 33hp and 40hp SA engines.  It is LEFT Hand rotation. This is important because the later, 1959 and up, engines were RH rotation.  10" diameter by 14" pitch.  Look at the photos and email with questions.  Thanks for looking.