I got a meter and PAT tester cheap at the local auction. with it was this mystery probe. I doesn't seem to be part of anything else that came in the box. its anodised aluminium case andan odd plug on theend the case has the markings KMR4. the plug has two contacts which have a co-axial pin in each one.thebusines end has 2 D shaped marks these appear to go through the head and each has a wire that goes to a resistor 100 and 160 one foreach side. the 100 Ohm is in series of one of the wires and the other one connects the other wire to ground.