The RF2561-000 is a polymeric positive temperature coefficient (PPTC) resettable fuse from the manufacturer Littelfuse. This device is designed to protect appliances and circuits from damage caused by excess current. It has a voltage rating of 30V, an operating current of 4A, and a maximum current of 40A. When current reaches a predetermined level, the PPTC resettable fuse will open up or trip, cutting off current to the system. Upon cooling, the device will reset itself and allow the flow of current to resume. This device is designed to protect against short-term current surges or faults, and can be used in a wide variety of applications, including automotive, industrial, and consumer electronics.