1 Pair Wire Piercing Probe Set,Insulation Piercing Clip Set with 4mm Banana Jacks Bottom for Multimeter Voltage Testing

These probes allow you to connect a meter to a wire that is in place and otherwise cannot be probed. They work by piercing the wire with a tiny needle. It does make a small hole in the insulation of the wire.To use the probe, you unscrew the black or red part of the probe to retract the needle. Then you pull back the spring-loaded part and insert the wire. Then you tighten the black or red part to force the needle to pierce the insulation on the wire.I tested the probes with two wires and an Ohmmeter. The black wire is a piece of 12 gauge wire with silicon insulation. The red wire is 18 gauge with PVC insulation. As you can tell from the meter, it detected a short between the two probes connected to the same wire. That confirms the probes had a good contact to the wire.I took close up photos of the wires so that you can see the tiny holes made by the probes. The holes are very hard to see on the black wire with silicon insulation because the silicone springs back. The PVC insulation does not spring back, and the holes are clearly visible. This is expected and the tiny holes do not present a hazard or risk unless you are using this in an environment where water could get into the wires. For those environments you might want to seal the holes with electrical tape, silicone tape, or heat shrink tubing.