Paul said:1 tube design for engines without thermostat. It should fit '57-'58 35hp engines (Without Thermostat for the '58!), '56 30hp engines, '62-'64 28hp engines and '65-'71 33hp engines. It will fit '70+ 40hp commercial engines but I don't recommend it because it uses an older bearing arrangement not found in the 40hp lower units.