The CH2 snaps onto the Phoenix meter body and allows measurements of #6 wire and smaller and currents up to 100 Amps AC (the highest amperage able to travel through a #6 wire). The Hook's patent pending technology significantly reduces the impact from current on adjacent wires by providing a virtual closed core inside the tip, which increases accuracy. The Worklight features isn't lost when exchanging the Phoenix base clamp head with The Hook, it also features a bright built-in Worklight, so wires inside dark enclusures are easy to see. The Hook works exclusively on the Phoenix Clamp Meter Series. Three year limited warranty.