The Siemon Testar-2 Two-Wire Adapter for RJ11 inserts directly onto 66 terminals on quick-connect block in simple, one-handed action. Probes easily, rapidly test connections, eliminating accidental shorting. For "M" and "E" blocks only. The adapter offers a modular jack on one side and comparable mating block on the other. Use matted surface on either side of probe tip for writing designations.