I came across this clip when I borrowed a telephone tone generator for analysing phone circuits. It is made by J S Popper and they will take a minimum order for $25 - which means you get three pairs. They slip onto banana plugs on your test leads and penetrate 10AWG through 26AWG wire insulation to permit readings to be taken. I have yet to receive them, but if the telephone version is anything to go by, this is a superb tool and one I have been looking for for quite a while. (My local Fluke distributor was clueless).
Essential for analysing those pesky electrical circuits in our cars.