SAE 10w30.
Look at your oil cap. The weight is on the cap.
The operator's manual for a 3020 should state which weights of oil should be used in specific temperatures. Generally a 30# oil should be used in the summer and a 10# oil in the winter. A Multi-weight oil such as 15W-40 can also be used in all seasons.
5W30
15/40
5w30
30 or 40 weight oil should be used.
The correct weight which should be 5w20 is listed in your owner's manaul.
SAE 20w50 100% synthetic oil.
10w-30
The manufacturer recommends that you use 10W-30 weight oil. 10 W-40 weight oil can be used in high mileage engines.
The manufacturer recommended 10W-30 weight oil in the 1979 Chevrolet Corvette. A heavier weight oil can be used in and older engine.
5W-30 preferred