Giles
Western Thunderer
They do indeed - usually inboard of the glasses. They hold the glasses and top and bottom castings together as a unit so you can slip them off for cleaning or replacing the gauge-glass. Lift them up a bit and pull the bottom off the cock and away the protector comes...... However, I can't find any details of triangular types at all! I don't even know if they have the metal painted sheet at the back!