If you slid it back on and made sure both ends of the spring were in both grooves of the needle plate, and it still falls off, look closely at the ends of the spring to make sure an end has not been broken off by a heavy hand. The one I bought had the needle plate loose with the machine. About a quarter inch had been broken off one end of the spring. In getting the spring out, I stripped the threads of the screw, so ordered it at the same time as the spring from Sew Classic. Shipping cost more than the two parts.