The oil filter cup wrench is a type of wrench that is shaped like a bowl or cup with notches on the edge that fit into the bottom of the oil filter. This wrench is used in conjunction with a ratchet or other tool to tighten or loosen the filter. The cup wrench is specifically designed for a particular size and type of filter, ensuring a very precise and firm grip. It is ideal for working in environments where the filter specification is known and flexibility is not required.