The probe is at the end of the loop of wire. You simply wrap it around whatever it is you want to temp, and pull it tight using fuel tubing or a zip tie. I've used it on nitro engines and electric motors. It does not need to be attached to the glow plug.

For $15 it is good quality, and it seems to be as accurate as any other temp guage. We have compaired the readings against several other temp guages, including the Duratrax guage and those overkill expensive guages people have had at the track.