Although sold by Sears, my mower engine is made by Tecumseh. There are several flywheel keys used on Tecumseh engines. Even if your mower is sold by Sears, you can take the Sears model number to your local mower shop and they can find the correct key for you. The key shown is part number 611004. It has a wider, thicker portion at one end. That end faces down on my engine. I was assured the key and flywheel would fit only when the key is in the correct position. (The photo is from Google Images.) A new key is about one dollar (US) in cost.