Based on position, we distinguish between two types of spring retainers. Top and bottom spring retainers. The upper spring retainer is the part that is located between the valves and the valve spring. A simpler version is a truly plate-like steel part through which the force of the spring acts on the valve. It is not always used for a lower spring retainer, it is most often needed to e.g. in the case of aluminum cylinder heads, the spring must not start the cylinder head on the receiving surface. There is a rotating spring retainer that allows the valve to turn a minimum with each spring compression and loosening, helping to avoid premature burnout caused by walking in one position - without rotation.