This is an affordable set of back probing test probes which serves dual purposes. One function is to back probe the wire at the rear of the wire harness/connector. This way, the tech avoids having to poke holes in the wire. The small diameter probe can slip into the back of the wore connector and make connection with the signal under test. The second function is the ability to pierce the wire if needed by using the supplied end piece adapter. Although piercing the wire is not advisable, sometimes it just cannot be avoided. This set of probes can work with most standard test lead kits in the field, such as ESI 142 and ESI 143 for example and other brands too. There are four probes included with this part number.