Worth it's weight in gold when a 2- or 4-cycle gas engine won't start, because the first thing you need to determine is whether the problem is no-spark/ignition or fuel supply/mixture. We were fooled ONCE into using a screwdriver to make the spark jump from the cable; DON'T try that at home - it hurts! This great little tool is the no-shock way to get the answer on ignition in about 30 seconds - BEFORE you work yourself to heart-attack stage pulling the rope on your lawnmower/chainsaw/snowblower or burning out the starter. Especially useful since many small engines now have low-oil cutoff or other ignition breakers. Rust-resistant chrome steel shaft, virtually unbreakable polycarbonate body and flexible rubber boot & cable. Internal bulb will last for years but is replaceable if necessary. Dimensions: 6" boot/cable, 5" shaft/light housing; 2.2 oz. Universal fit for all 2- or 4-stroke, single or multi-cylinder gasoline engines.