Federal regulations are phasing in lead free fixtures. This means more and more of the guts are being made of plastic. On mine, before that started, the body is a huge hunk of cast brass - the thing weighs probably close to 10# (it's an external mount tub/shower, now discontinued, at least in the USA). I chose this style because there's a pocket door behind this wall, and I couldn't use the depth to mount a 'normal' valve. The fixture has the volume, spout, diverter, and temp in one solid unit. The actual thermostatic control portion is the same or similar to other designs in the line, though, and hopefully, should provide an idea of how yours would work. The actual knobs are plastic, though, but still look good. If they were metal, it's possible they could get quite hot after an extended tub fill, but normally, that wouldn't be an issue.