There are two types of heat shields for these units. There are little white ones that clip onto the flexible cooling tubes. The other shields are larger black metal plates that screw onto the inside of the plastic endplates of the head. It seems like the white clamp-on shields were only produced for a little while (few heads have them - I have only seen them on the early 300w heads). The larger black metal shields are on every 300w head that I have ever come across (they protect the plastic sides from melting - don't know if you can get by without these...they should be easy to make if your head doesn't have them)