Heats and melts plastic (I don't use the soldering iron that comes with it). It's a small instrument, everything is small. The sponge size is 3/4 x 1 1/4 inches, the diameter of the temporary dial is 8mm, so the font size of the digital characters on this dial is probably a 3 or 4. The indicator light is very useful to remind you that it is on. and hot. Great price for a small tool for my occasional use in small workshops.