Pull start fits the 40cc 4-stroke engines like the ones on our pocket bikes and dirt bikes. Fits most brands. Take off your old pull start and see if yours looks like this. The listing is for ONE pull start even though the picture shows two so you can see the front and back at the same time.
If you took off your pull start, check that you can turn the flywheel with your hand (clockwise). If it's not turning, the problem might be not the pull start but something else, like a jammed piston (hopefully not), or a busted clutch (likely) on the opposite side of the engine.